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 $114.87   9.712%   $126.0262   $126.03   $126.05   $126.00  
  Purchase #2 $241.98   3.185%   $249.6871   $249.69   $249.70   $249.70  
  Purchase #3 $28.61   8.818%   $31.1328   $31.13   $31.15   $31.10  
  Purchase #4 $133.82   13.731%   $152.1948   $152.19   $152.20   $152.20  
  Purchase #5 $53.84   11.772%   $60.178   $60.18   $60.20   $60.20  
  Purchase #6 $193.73   6.153%   $205.6502   $205.65   $205.65   $205.70  
  Purchase #7 $67.82   6.511%   $72.2358   $72.24   $72.25   $72.20  
  7 purchase totals = $834.67       $897.1049   $897.11   $897.20   $897.10