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 $61.30   11.763%   $68.5107   $68.51   $68.50   $68.50  
  Purchase #2 $203.48   4.324%   $212.2785   $212.28   $212.30   $212.30  
  Purchase #3 $52.71   8.649%   $57.2689   $57.27   $57.25   $57.30  
  Purchase #4 $85.89   9.249%   $93.834   $93.83   $93.85   $93.80  
  Purchase #5 $49.55   3.179%   $51.1252   $51.13   $51.15   $51.10  
  Purchase #6 $130.76   8.292%   $141.6026   $141.60   $141.60   $141.60  
  Purchase #7 $97.55   13.761%   $110.9739   $110.97   $110.95   $111.00  
  7 purchase totals = $681.24       $735.5938   $735.59   $735.60   $735.60