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 $87.63   12.395%   $98.4917   $98.49   $98.50   $98.50  
  Purchase #2 $243.33   11.177%   $270.527   $270.53   $270.55   $270.50  
  Purchase #3 $150.79   8.667%   $163.859   $163.86   $163.85   $163.90  
  Purchase #4 $113.38   11.649%   $126.5876   $126.59   $126.60   $126.60  
  Purchase #5 $110.66   7.750%   $119.2362   $119.24   $119.25   $119.20  
  Purchase #6 $183.66   13.826%   $209.0528   $209.05   $209.05   $209.10  
  Purchase #7 $104.67   8.614%   $113.6863   $113.69   $113.70   $113.70  
  7 purchase totals = $994.12       $1,101.4406   $1,101.45   $1,101.50   $1,101.50