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 $67.54   11.802%   $75.5111   $75.51   $75.50   $75.50  
  Purchase #2 $98.67   13.303%   $111.7961   $111.80   $111.80   $111.80  
  Purchase #3 $154.25   3.555%   $159.7336   $159.73   $159.75   $159.70  
  Purchase #4 $26.28   6.163%   $27.8996   $27.90   $27.90   $27.90  
  Purchase #5 $162.26   5.337%   $170.9198   $170.92   $170.90   $170.90  
  Purchase #6 $110.64   7.240%   $118.6503   $118.65   $118.65   $118.70  
  Purchase #7 $111.56   4.527%   $116.6103   $116.61   $116.60   $116.60  
  7 purchase totals = $731.20       $781.1208   $781.12   $781.10   $781.10