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 $221.83   7.129%   $237.6443   $237.64   $237.65   $237.60  
  Purchase #2 $93.82   11.664%   $104.7632   $104.76   $104.75   $104.80  
  Purchase #3 $171.53   3.236%   $177.0807   $177.08   $177.10   $177.10  
  Purchase #4 $192.96   11.505%   $215.16   $215.16   $215.15   $215.20  
  Purchase #5 $186.74   5.839%   $197.6437   $197.64   $197.65   $197.60  
  Purchase #6 $188.90   11.324%   $210.291   $210.29   $210.30   $210.30  
  Purchase #7 $245.72   10.752%   $272.1398   $272.14   $272.15   $272.10  
  7 purchase totals = $1,301.50       $1,414.7227   $1,414.71   $1,414.75   $1,414.70