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 $180.96   13.413%   $205.2322   $205.23   $205.25   $205.20  
  Purchase #2 $167.87   13.395%   $190.3562   $190.36   $190.35   $190.40  
  Purchase #3 $221.35   11.434%   $246.6592   $246.66   $246.65   $246.70  
  Purchase #4 $63.91   4.487%   $66.7776   $66.78   $66.80   $66.80  
  Purchase #5 $44.72   5.518%   $47.1876   $47.19   $47.20   $47.20  
  Purchase #6 $35.36   5.564%   $37.3274   $37.33   $37.35   $37.30  
  Purchase #7 $136.38   9.517%   $149.3593   $149.36   $149.35   $149.40  
  7 purchase totals = $850.55       $942.8995   $942.91   $942.95   $943.00