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 $26.58   11.803%   $29.7172   $29.72   $29.70   $29.70  
  Purchase #2 $163.82   12.176%   $183.7667   $183.77   $183.75   $183.80  
  Purchase #3 $132.89   10.459%   $146.789   $146.79   $146.80   $146.80  
  Purchase #4 $60.53   6.803%   $64.6479   $64.65   $64.65   $64.60  
  Purchase #5 $134.27   3.769%   $139.3306   $139.33   $139.35   $139.30  
  Purchase #6 $50.67   9.151%   $55.3068   $55.31   $55.30   $55.30  
  Purchase #7 $131.78   7.302%   $141.4026   $141.40   $141.40   $141.40  
  7 purchase totals = $700.54       $760.9608   $760.97   $760.95   $760.90