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 $121.65   3.450%   $125.8469   $125.85   $125.85   $125.80  
  Purchase #2 $22.99   12.606%   $25.8881   $25.89   $25.90   $25.90  
  Purchase #3 $105.82   10.327%   $116.748   $116.75   $116.75   $116.70  
  Purchase #4 $75.31   8.156%   $81.4523   $81.45   $81.45   $81.50  
  Purchase #5 $129.26   7.345%   $138.7541   $138.75   $138.75   $138.80  
  Purchase #6 $126.44   9.435%   $138.3696   $138.37   $138.35   $138.40  
  Purchase #7 $101.28   11.125%   $112.5474   $112.55   $112.55   $112.50  
  7 purchase totals = $682.75       $739.6064   $739.61   $739.60   $739.60