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 $91.56   6.204%   $97.2404   $97.24   $97.25   $97.20  
  Purchase #2 $205.33   10.795%   $227.4954   $227.50   $227.50   $227.50  
  Purchase #3 $136.77   3.262%   $141.2314   $141.23   $141.25   $141.20  
  Purchase #4 $151.67   3.464%   $156.9238   $156.92   $156.90   $156.90  
  Purchase #5 $115.91   10.808%   $128.4376   $128.44   $128.45   $128.40  
  Purchase #6 $125.28   10.647%   $138.6186   $138.62   $138.60   $138.60  
  Purchase #7 $132.44   8.718%   $143.9861   $143.99   $144.00   $144.00  
  7 purchase totals = $958.96       $1,033.9333   $1,033.94   $1,033.95   $1,033.80