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 $69.66   9.366%   $76.1844   $76.18   $76.20   $76.20  
  Purchase #2 $60.33   3.709%   $62.5676   $62.57   $62.55   $62.60  
  Purchase #3 $225.33   11.539%   $251.3308   $251.33   $251.35   $251.30  
  Purchase #4 $127.26   8.839%   $138.5085   $138.51   $138.50   $138.50  
  Purchase #5 $88.56   9.248%   $96.75   $96.75   $96.75   $96.80  
  Purchase #6 $98.71   5.778%   $104.4135   $104.41   $104.40   $104.40  
  Purchase #7 $144.95   7.105%   $155.2487   $155.25   $155.25   $155.20  
  7 purchase totals = $814.80       $885.0035   $885.00   $885.00   $885.00