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 $58.88   13.758%   $66.9807   $66.98   $67.00   $67.00  
  Purchase #2 $70.57   4.653%   $73.8536   $73.85   $73.85   $73.90  
  Purchase #3 $90.78   12.749%   $102.3535   $102.35   $102.35   $102.40  
  Purchase #4 $78.81   5.346%   $83.0232   $83.02   $83.00   $83.00  
  Purchase #5 $150.99   4.614%   $157.9567   $157.96   $157.95   $158.00  
  Purchase #6 $88.59   12.535%   $99.6948   $99.69   $99.70   $99.70  
  Purchase #7 $8.74   7.277%   $9.376   $9.38   $9.40   $9.40  
  7 purchase totals = $547.36       $593.2385   $593.23   $593.25   $593.40