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 $69.68   8.145%   $75.3554   $75.36   $75.35   $75.40  
  Purchase #2 $104.55   9.426%   $114.4049   $114.40   $114.40   $114.40  
  Purchase #3 $110.69   9.152%   $120.8203   $120.82   $120.80   $120.80  
  Purchase #4 $65.49   7.113%   $70.1483   $70.15   $70.15   $70.10  
  Purchase #5 $169.57   8.248%   $183.5561   $183.56   $183.55   $183.60  
  Purchase #6 $173.98   5.119%   $182.886   $182.89   $182.90   $182.90  
  Purchase #7 $241.95   3.714%   $250.936   $250.94   $250.95   $250.90  
  7 purchase totals = $935.91       $998.1070   $998.12   $998.10   $998.10