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 $57.52   5.329%   $60.5852   $60.59   $60.60   $60.60  
  Purchase #2 $116.56   4.806%   $122.1619   $122.16   $122.15   $122.20  
  Purchase #3 $148.26   9.467%   $162.2958   $162.30   $162.30   $162.30  
  Purchase #4 $25.77   5.712%   $27.242   $27.24   $27.25   $27.20  
  Purchase #5 $40.74   11.178%   $45.2939   $45.29   $45.30   $45.30  
  Purchase #6 $11.82   12.217%   $13.264   $13.26   $13.25   $13.30  
  Purchase #7 $163.37   11.804%   $182.6542   $182.65   $182.65   $182.70  
  7 purchase totals = $564.04       $613.4970   $613.49   $613.50   $613.60