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 $67.42   13.805%   $76.7273   $76.73   $76.75   $76.70  
  Purchase #2 $218.63   8.163%   $236.4768   $236.48   $236.50   $236.50  
  Purchase #3 $123.68   9.826%   $135.8328   $135.83   $135.85   $135.80  
  Purchase #4 $106.77   9.732%   $117.1609   $117.16   $117.15   $117.20  
  Purchase #5 $98.92   6.579%   $105.4279   $105.43   $105.45   $105.40  
  Purchase #6 $234.28   6.203%   $248.8124   $248.81   $248.80   $248.80  
  Purchase #7 $58.77   6.753%   $62.7387   $62.74   $62.75   $62.70  
  7 purchase totals = $908.47       $983.1768   $983.18   $983.25   $983.10