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 $209.95   3.135%   $216.5319   $216.53   $216.55   $216.50  
  Purchase #2 $183.55   5.817%   $194.2271   $194.23   $194.25   $194.20  
  Purchase #3 $106.95   8.798%   $116.3595   $116.36   $116.35   $116.40  
  Purchase #4 $94.64   5.249%   $99.6077   $99.61   $99.60   $99.60  
  Purchase #5 $229.59   5.240%   $241.6205   $241.62   $241.60   $241.60  
  Purchase #6 $10.25   12.321%   $11.5129   $11.51   $11.50   $11.50  
  Purchase #7 $104.76   13.710%   $119.1226   $119.12   $119.10   $119.10  
  7 purchase totals = $939.69       $998.9822   $998.98   $998.95   $998.90