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 $245.67   5.392%   $258.9165   $258.92   $258.90   $258.90  
  Purchase #2 $20.67   9.506%   $22.6349   $22.63   $22.65   $22.60  
  Purchase #3 $101.76   10.499%   $112.4438   $112.44   $112.45   $112.40  
  Purchase #4 $177.54   9.770%   $194.8857   $194.89   $194.90   $194.90  
  Purchase #5 $71.99   7.359%   $77.2877   $77.29   $77.30   $77.30  
  Purchase #6 $61.39   11.198%   $68.2645   $68.26   $68.25   $68.30  
  Purchase #7 $244.86   10.756%   $271.1971   $271.20   $271.20   $271.20  
  7 purchase totals = $923.88       $1,005.6302   $1,005.63   $1,005.65   $1,005.60