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 $82.41   7.562%   $88.6418   $88.64   $88.65   $88.60  
  Purchase #2 $82.60   12.294%   $92.7548   $92.75   $92.75   $92.80  
  Purchase #3 $68.78   6.333%   $73.1358   $73.14   $73.15   $73.10  
  Purchase #4 $241.96   8.645%   $262.8774   $262.88   $262.90   $262.90  
  Purchase #5 $157.62   12.329%   $177.053   $177.05   $177.05   $177.10  
  Purchase #6 $206.68   3.848%   $214.633   $214.63   $214.65   $214.60  
  Purchase #7 $232.67   9.738%   $255.3274   $255.33   $255.35   $255.30  
  7 purchase totals = $1,072.72       $1,164.4232   $1,164.42   $1,164.50   $1,164.40