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 $213.74   13.668%   $242.954   $242.95   $242.95   $243.00  
  Purchase #2 $26.34   11.295%   $29.3151   $29.32   $29.30   $29.30  
  Purchase #3 $72.42   4.335%   $75.5594   $75.56   $75.55   $75.60  
  Purchase #4 $221.96   6.139%   $235.5861   $235.59   $235.60   $235.60  
  Purchase #5 $190.75   13.113%   $215.763   $215.76   $215.75   $215.80  
  Purchase #6 $132.58   7.662%   $142.7383   $142.74   $142.75   $142.70  
  Purchase #7 $8.97   7.766%   $9.6666   $9.67   $9.65   $9.70  
  7 purchase totals = $866.76       $951.5825   $951.59   $951.55   $951.70