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 $205.36   9.819%   $225.5243   $225.52   $225.50   $225.50  
  Purchase #2 $11.78   10.421%   $13.0076   $13.01   $13.00   $13.00  
  Purchase #3 $42.39   9.259%   $46.3149   $46.31   $46.30   $46.30  
  Purchase #4 $90.77   6.457%   $96.631   $96.63   $96.65   $96.60  
  Purchase #5 $213.83   11.298%   $237.9885   $237.99   $238.00   $238.00  
  Purchase #6 $159.85   4.576%   $167.1647   $167.16   $167.15   $167.20  
  Purchase #7 $22.93   13.344%   $25.9898   $25.99   $26.00   $26.00  
  7 purchase totals = $746.91       $812.6208   $812.61   $812.60   $812.60