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 $244.52   7.128%   $261.9494   $261.95   $261.95   $261.90  
  Purchase #2 $151.25   10.536%   $167.1857   $167.19   $167.20   $167.20  
  Purchase #3 $53.29   9.567%   $58.3883   $58.39   $58.40   $58.40  
  Purchase #4 $119.57   4.508%   $124.9602   $124.96   $124.95   $125.00  
  Purchase #5 $233.97   5.214%   $246.1692   $246.17   $246.15   $246.20  
  Purchase #6 $71.66   3.469%   $74.1459   $74.15   $74.15   $74.10  
  Purchase #7 $78.90   11.173%   $87.7155   $87.72   $87.70   $87.70  
  7 purchase totals = $953.16       $1,020.5142   $1,020.53   $1,020.50   $1,020.50