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 $221.87   11.660%   $247.74   $247.74   $247.75   $247.70  
  Purchase #2 $67.30   10.641%   $74.4614   $74.46   $74.45   $74.50  
  Purchase #3 $60.71   11.590%   $67.7463   $67.75   $67.75   $67.70  
  Purchase #4 $143.89   8.107%   $155.5552   $155.56   $155.55   $155.60  
  Purchase #5 $146.47   13.198%   $165.8011   $165.80   $165.80   $165.80  
  Purchase #6 $63.52   3.181%   $65.5406   $65.54   $65.55   $65.50  
  Purchase #7 $153.67   13.670%   $174.6767   $174.68   $174.70   $174.70  
  7 purchase totals = $857.43       $951.5213   $951.53   $951.55   $951.50