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 $61.91   11.741%   $69.1789   $69.18   $69.20   $69.20  
  Purchase #2 $231.52   10.699%   $256.2903   $256.29   $256.30   $256.30  
  Purchase #3 $38.38   6.401%   $40.8367   $40.84   $40.85   $40.80  
  Purchase #4 $143.64   9.401%   $157.1436   $157.14   $157.15   $157.10  
  Purchase #5 $37.67   5.293%   $39.6639   $39.66   $39.65   $39.70  
  Purchase #6 $234.28   6.161%   $248.714   $248.71   $248.70   $248.70  
  Purchase #7 $129.97   7.796%   $140.1025   $140.10   $140.10   $140.10  
  7 purchase totals = $877.37       $951.9299   $951.92   $951.95   $951.90