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 $129.43   5.554%   $136.6185   $136.62   $136.60   $136.60  
  Purchase #2 $82.43   9.106%   $89.9361   $89.94   $89.95   $89.90  
  Purchase #3 $212.25   6.773%   $226.6257   $226.63   $226.65   $226.60  
  Purchase #4 $158.87   11.201%   $176.665   $176.67   $176.65   $176.70  
  Purchase #5 $87.64   5.286%   $92.2727   $92.27   $92.25   $92.30  
  Purchase #6 $241.86   10.657%   $267.635   $267.64   $267.65   $267.60  
  Purchase #7 $197.77   4.541%   $206.7507   $206.75   $206.75   $206.80  
  7 purchase totals = $1,110.25       $1,196.5037   $1,196.52   $1,196.50   $1,196.50