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 $73.65   3.783%   $76.4362   $76.44   $76.45   $76.40  
  Purchase #2 $35.45   4.185%   $36.9336   $36.93   $36.95   $36.90  
  Purchase #3 $249.58   4.219%   $260.1098   $260.11   $260.10   $260.10  
  Purchase #4 $64.37   8.646%   $69.9354   $69.94   $69.95   $69.90  
  Purchase #5 $25.63   10.254%   $28.2581   $28.26   $28.25   $28.30  
  Purchase #6 $44.41   11.682%   $49.598   $49.60   $49.60   $49.60  
  Purchase #7 $60.39   8.738%   $65.6669   $65.67   $65.65   $65.70  
  7 purchase totals = $553.48       $586.9380   $586.95   $586.95   $586.90