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 $201.65   12.560%   $226.9772   $226.98   $227.00   $227.00  
  Purchase #2 $95.77   9.274%   $104.6517   $104.65   $104.65   $104.70  
  Purchase #3 $79.60   10.704%   $88.1204   $88.12   $88.10   $88.10  
  Purchase #4 $216.84   10.177%   $238.9078   $238.91   $238.90   $238.90  
  Purchase #5 $117.87   10.856%   $130.666   $130.67   $130.65   $130.70  
  Purchase #6 $69.60   12.503%   $78.3021   $78.30   $78.30   $78.30  
  Purchase #7 $207.99   4.399%   $217.1395   $217.14   $217.15   $217.10  
  7 purchase totals = $989.32       $1,084.7647   $1,084.77   $1,084.75   $1,084.80