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 $194.47   12.615%   $219.0024   $219.00   $219.00   $219.00  
  Purchase #2 $101.42   10.445%   $112.0133   $112.01   $112.00   $112.00  
  Purchase #3 $72.52   4.626%   $75.8748   $75.87   $75.85   $75.90  
  Purchase #4 $47.31   13.258%   $53.5824   $53.58   $53.60   $53.60  
  Purchase #5 $103.91   11.373%   $115.7277   $115.73   $115.75   $115.70  
  Purchase #6 $134.81   4.571%   $140.9722   $140.97   $140.95   $141.00  
  Purchase #7 $216.54   8.130%   $234.1447   $234.14   $234.15   $234.10  
  7 purchase totals = $870.98       $951.3175   $951.30   $951.30   $951.30