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 $14.88   6.669%   $15.8723   $15.87   $15.85   $15.90  
  Purchase #2 $176.59   4.485%   $184.5101   $184.51   $184.50   $184.50  
  Purchase #3 $24.96   7.132%   $26.7401   $26.74   $26.75   $26.70  
  Purchase #4 $56.99   13.664%   $64.7771   $64.78   $64.80   $64.80  
  Purchase #5 $95.80   5.141%   $100.7251   $100.73   $100.75   $100.70  
  Purchase #6 $246.53   9.265%   $269.371   $269.37   $269.35   $269.40  
  Purchase #7 $191.47   12.418%   $215.2467   $215.25   $215.25   $215.20  
  7 purchase totals = $807.22       $877.2424   $877.25   $877.25   $877.20