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 $60.88   12.530%   $68.5083   $68.51   $68.50   $68.50  
  Purchase #2 $164.67   9.511%   $180.3318   $180.33   $180.35   $180.30  
  Purchase #3 $240.54   7.179%   $257.8084   $257.81   $257.80   $257.80  
  Purchase #4 $206.61   12.296%   $232.0148   $232.01   $232.00   $232.00  
  Purchase #5 $10.62   4.278%   $11.0743   $11.07   $11.05   $11.10  
  Purchase #6 $26.34   12.416%   $29.6104   $29.61   $29.60   $29.60  
  Purchase #7 $165.37   4.655%   $173.068   $173.07   $173.05   $173.10  
  7 purchase totals = $875.03       $952.4160   $952.41   $952.35   $952.40