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 $243.92   11.102%   $271   $271.00   $271.00   $271.00  
  Purchase #2 $154.71   10.305%   $170.6529   $170.65   $170.65   $170.70  
  Purchase #3 $64.66   8.175%   $69.946   $69.95   $69.95   $69.90  
  Purchase #4 $215.53   8.253%   $233.3177   $233.32   $233.30   $233.30  
  Purchase #5 $126.45   4.218%   $131.7837   $131.78   $131.80   $131.80  
  Purchase #6 $220.46   7.238%   $236.4169   $236.42   $236.40   $236.40  
  Purchase #7 $209.62   5.671%   $221.5076   $221.51   $221.50   $221.50  
  7 purchase totals = $1,235.35       $1,334.6248   $1,334.63   $1,334.60   $1,334.60