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 $87.50   12.269%   $98.2354   $98.24   $98.25   $98.20  
  Purchase #2 $105.91   11.539%   $118.131   $118.13   $118.15   $118.10  
  Purchase #3 $232.75   12.187%   $261.1152   $261.12   $261.10   $261.10  
  Purchase #4 $147.73   10.265%   $162.8945   $162.89   $162.90   $162.90  
  Purchase #5 $106.30   12.267%   $119.3398   $119.34   $119.35   $119.30  
  Purchase #6 $158.65   4.653%   $166.032   $166.03   $166.05   $166.00  
  Purchase #7 $67.59   12.161%   $75.8096   $75.81   $75.80   $75.80  
  7 purchase totals = $906.43       $1,001.5575   $1,001.56   $1,001.60   $1,001.40