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 $61.89   4.148%   $64.4572   $64.46   $64.45   $64.50  
  Purchase #2 $198.99   10.675%   $220.2322   $220.23   $220.25   $220.20  
  Purchase #3 $16.28   12.342%   $18.2893   $18.29   $18.30   $18.30  
  Purchase #4 $195.53   13.210%   $221.3595   $221.36   $221.35   $221.40  
  Purchase #5 $174.80   10.374%   $192.9338   $192.93   $192.95   $192.90  
  Purchase #6 $215.46   12.511%   $242.4162   $242.42   $242.40   $242.40  
  Purchase #7 $129.48   13.165%   $146.526   $146.53   $146.55   $146.50  
  7 purchase totals = $992.43       $1,106.2142   $1,106.22   $1,106.25   $1,106.20