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 $52.83   8.439%   $57.2883   $57.29   $57.30   $57.30  
  Purchase #2 $194.46   13.168%   $220.0665   $220.07   $220.05   $220.10  
  Purchase #3 $162.35   7.480%   $174.4938   $174.49   $174.50   $174.50  
  Purchase #4 $224.72   13.526%   $255.1156   $255.12   $255.10   $255.10  
  Purchase #5 $94.92   9.532%   $103.9678   $103.97   $103.95   $104.00  
  Purchase #6 $136.86   12.605%   $154.1112   $154.11   $154.10   $154.10  
  Purchase #7 $181.90   3.511%   $188.2865   $188.29   $188.30   $188.30  
  7 purchase totals = $1,048.04       $1,153.3297   $1,153.34   $1,153.30   $1,153.40