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 $154.50   10.138%   $170.1632   $170.16   $170.15   $170.20  
  Purchase #2 $134.84   10.216%   $148.6153   $148.62   $148.60   $148.60  
  Purchase #3 $141.60   5.764%   $149.7618   $149.76   $149.75   $149.80  
  Purchase #4 $143.58   10.579%   $158.7693   $158.77   $158.75   $158.80  
  Purchase #5 $81.73   12.501%   $91.9471   $91.95   $91.95   $91.90  
  Purchase #6 $71.56   7.859%   $77.1839   $77.18   $77.20   $77.20  
  Purchase #7 $51.82   7.655%   $55.7868   $55.79   $55.80   $55.80  
  7 purchase totals = $779.63       $852.2274   $852.23   $852.20   $852.30