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 $175.34   13.694%   $199.3511   $199.35   $199.35   $199.40  
  Purchase #2 $171.51   7.127%   $183.7335   $183.73   $183.75   $183.70  
  Purchase #3 $84.39   12.571%   $94.9987   $95.00   $95.00   $95.00  
  Purchase #4 $133.26   4.188%   $138.8409   $138.84   $138.85   $138.80  
  Purchase #5 $40.77   11.708%   $45.5434   $45.54   $45.55   $45.50  
  Purchase #6 $48.40   4.590%   $50.6216   $50.62   $50.60   $50.60  
  Purchase #7 $87.97   5.372%   $92.6957   $92.70   $92.70   $92.70  
  7 purchase totals = $741.64       $805.7849   $805.78   $805.80   $805.70