Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $140.28   12.282%   $157.5092   $157.51   $157.50   $157.50  
  Purchase #2 $213.67   12.624%   $240.6437   $240.64   $240.65   $240.60  
  Purchase #3 $220.43   10.638%   $243.8793   $243.88   $243.90   $243.90  
  Purchase #4 $237.99   12.548%   $267.853   $267.85   $267.85   $267.90  
  Purchase #5 $188.52   4.828%   $197.6217   $197.62   $197.60   $197.60  
  Purchase #6 $231.29   12.570%   $260.3632   $260.36   $260.35   $260.40  
  Purchase #7 $227.44   11.127%   $252.7472   $252.75   $252.75   $252.70  
  7 purchase totals = $1,459.62       $1,620.6173   $1,620.61   $1,620.60   $1,620.60