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 $68.38   10.746%   $75.7281   $75.73   $75.75   $75.70  
  Purchase #2 $123.74   9.386%   $135.3542   $135.35   $135.35   $135.40  
  Purchase #3 $231.44   3.752%   $240.1236   $240.12   $240.10   $240.10  
  Purchase #4 $132.32   12.512%   $148.8759   $148.88   $148.90   $148.90  
  Purchase #5 $131.99   11.521%   $147.1966   $147.20   $147.20   $147.20  
  Purchase #6 $55.38   7.475%   $59.5197   $59.52   $59.50   $59.50  
  Purchase #7 $239.25   5.492%   $252.3896   $252.39   $252.40   $252.40  
  7 purchase totals = $982.50       $1,059.1877   $1,059.19   $1,059.20   $1,059.20