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 $238.53   13.501%   $270.7339   $270.73   $270.75   $270.70  
  Purchase #2 $98.57   4.240%   $102.7494   $102.75   $102.75   $102.70  
  Purchase #3 $118.27   6.269%   $125.6843   $125.68   $125.70   $125.70  
  Purchase #4 $232.82   9.151%   $254.1254   $254.13   $254.15   $254.10  
  Purchase #5 $175.45   13.258%   $198.7112   $198.71   $198.70   $198.70  
  Purchase #6 $119.56   11.624%   $133.4577   $133.46   $133.45   $133.50  
  Purchase #7 $186.93   10.598%   $206.7408   $206.74   $206.75   $206.70  
  7 purchase totals = $1,170.13       $1,292.2027   $1,292.20   $1,292.25   $1,292.10