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 $82.78   12.768%   $93.3494   $93.35   $93.35   $93.30  
  Purchase #2 $143.37   5.622%   $151.4303   $151.43   $151.45   $151.40  
  Purchase #3 $182.74   13.188%   $206.8398   $206.84   $206.85   $206.80  
  Purchase #4 $195.39   10.477%   $215.861   $215.86   $215.85   $215.90  
  Purchase #5 $77.73   13.525%   $88.243   $88.24   $88.25   $88.20  
  Purchase #6 $199.69   9.367%   $218.395   $218.40   $218.40   $218.40  
  Purchase #7 $10.52   12.762%   $11.8626   $11.86   $11.85   $11.90  
  7 purchase totals = $892.22       $985.9811   $985.98   $986.00   $985.90