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 $113.48   7.397%   $121.8741   $121.87   $121.85   $121.90  
  Purchase #2 $116.39   8.792%   $126.623   $126.62   $126.60   $126.60  
  Purchase #3 $217.99   11.518%   $243.0981   $243.10   $243.10   $243.10  
  Purchase #4 $240.72   8.545%   $261.2895   $261.29   $261.30   $261.30  
  Purchase #5 $221.87   4.631%   $232.1448   $232.14   $232.15   $232.10  
  Purchase #6 $84.75   5.454%   $89.3723   $89.37   $89.35   $89.40  
  Purchase #7 $9.31   13.779%   $10.5928   $10.59   $10.60   $10.60  
  7 purchase totals = $1,004.51       $1,084.9946   $1,084.98   $1,084.95   $1,085.00