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 $215.38   13.105%   $243.6055   $243.61   $243.60   $243.60  
  Purchase #2 $103.78   10.674%   $114.8575   $114.86   $114.85   $114.90  
  Purchase #3 $36.87   5.531%   $38.9093   $38.91   $38.90   $38.90  
  Purchase #4 $138.72   7.449%   $149.0533   $149.05   $149.05   $149.10  
  Purchase #5 $128.36   4.621%   $134.2915   $134.29   $134.30   $134.30  
  Purchase #6 $71.26   13.701%   $81.0233   $81.02   $81.00   $81.00  
  Purchase #7 $168.80   10.660%   $186.7941   $186.79   $186.80   $186.80  
  7 purchase totals = $863.17       $948.5345   $948.53   $948.50   $948.60