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 $148.78   6.448%   $158.3733   $158.37   $158.35   $158.40  
  Purchase #2 $122.66   9.146%   $133.8785   $133.88   $133.90   $133.90  
  Purchase #3 $218.53   7.489%   $234.8957   $234.90   $234.90   $234.90  
  Purchase #4 $66.53   13.424%   $75.461   $75.46   $75.45   $75.50  
  Purchase #5 $15.85   4.161%   $16.5095   $16.51   $16.50   $16.50  
  Purchase #6 $208.34   3.160%   $214.9235   $214.92   $214.90   $214.90  
  Purchase #7 $209.35   5.813%   $221.5195   $221.52   $221.50   $221.50  
  7 purchase totals = $990.04       $1,055.5610   $1,055.56   $1,055.50   $1,055.60