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 $224.94   11.388%   $250.5562   $250.56   $250.55   $250.60  
  Purchase #2 $188.82   11.478%   $210.4928   $210.49   $210.50   $210.50  
  Purchase #3 $117.32   8.315%   $127.0752   $127.08   $127.10   $127.10  
  Purchase #4 $195.72   3.358%   $202.2923   $202.29   $202.30   $202.30  
  Purchase #5 $5.72   4.205%   $5.9605   $5.96   $5.95   $6.00  
  Purchase #6 $56.43   12.185%   $63.306   $63.31   $63.30   $63.30  
  Purchase #7 $67.28   12.545%   $75.7203   $75.72   $75.70   $75.70  
  7 purchase totals = $856.23       $935.4033   $935.41   $935.40   $935.50