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 $88.48   6.810%   $94.5055   $94.51   $94.50   $94.50  
  Purchase #2 $237.96   8.569%   $258.3508   $258.35   $258.35   $258.40  
  Purchase #3 $169.37   6.807%   $180.899   $180.90   $180.90   $180.90  
  Purchase #4 $149.37   13.239%   $169.1451   $169.15   $169.15   $169.10  
  Purchase #5 $68.41   10.808%   $75.8038   $75.80   $75.80   $75.80  
  Purchase #6 $123.51   11.222%   $137.3703   $137.37   $137.35   $137.40  
  Purchase #7 $113.41   10.709%   $125.5551   $125.56   $125.55   $125.60  
  7 purchase totals = $950.51       $1,041.6296   $1,041.64   $1,041.60   $1,041.70