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 $125.69   9.528%   $137.6657   $137.67   $137.65   $137.70  
  Purchase #2 $191.96   10.155%   $211.4535   $211.45   $211.45   $211.50  
  Purchase #3 $15.80   4.608%   $16.5281   $16.53   $16.55   $16.50  
  Purchase #4 $73.34   7.754%   $79.0268   $79.03   $79.05   $79.00  
  Purchase #5 $107.89   10.277%   $118.9779   $118.98   $119.00   $119.00  
  Purchase #6 $233.63   11.777%   $261.1446   $261.14   $261.15   $261.10  
  Purchase #7 $58.61   9.682%   $64.2846   $64.28   $64.30   $64.30  
  7 purchase totals = $806.92       $889.0812   $889.08   $889.15   $889.10