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 $37.98   8.220%   $41.102   $41.10   $41.10   $41.10  
  Purchase #2 $166.62   6.163%   $176.8888   $176.89   $176.90   $176.90  
  Purchase #3 $139.49   10.179%   $153.6887   $153.69   $153.70   $153.70  
  Purchase #4 $237.43   10.756%   $262.968   $262.97   $262.95   $263.00  
  Purchase #5 $195.39   7.420%   $209.8879   $209.89   $209.90   $209.90  
  Purchase #6 $158.47   6.601%   $168.9306   $168.93   $168.95   $168.90  
  Purchase #7 $15.66   6.394%   $16.6613   $16.66   $16.65   $16.70  
  7 purchase totals = $951.04       $1,030.1273   $1,030.13   $1,030.15   $1,030.20