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 $175.58   11.602%   $195.9508   $195.95   $195.95   $196.00  
  Purchase #2 $119.74   3.274%   $123.6603   $123.66   $123.65   $123.70  
  Purchase #3 $35.86   11.254%   $39.8957   $39.90   $39.90   $39.90  
  Purchase #4 $20.62   5.504%   $21.7549   $21.75   $21.75   $21.80  
  Purchase #5 $59.32   8.616%   $64.431   $64.43   $64.45   $64.40  
  Purchase #6 $149.54   12.433%   $168.1323   $168.13   $168.15   $168.10  
  Purchase #7 $208.56   13.490%   $236.6947   $236.69   $236.70   $236.70  
  7 purchase totals = $769.22       $850.5197   $850.51   $850.55   $850.60