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 $56.60   10.105%   $62.3194   $62.32   $62.30   $62.30  
  Purchase #2 $237.46   8.429%   $257.4755   $257.48   $257.50   $257.50  
  Purchase #3 $151.86   8.668%   $165.0232   $165.02   $165.00   $165.00  
  Purchase #4 $44.28   3.173%   $45.685   $45.69   $45.70   $45.70  
  Purchase #5 $41.35   7.606%   $44.4951   $44.50   $44.50   $44.50  
  Purchase #6 $160.49   12.735%   $180.9284   $180.93   $180.95   $180.90  
  Purchase #7 $183.57   4.355%   $191.5645   $191.56   $191.55   $191.60  
  7 purchase totals = $875.61       $947.4911   $947.50   $947.50   $947.50