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 $246.97   7.796%   $266.2238   $266.22   $266.20   $266.20  
  Purchase #2 $195.33   11.440%   $217.6758   $217.68   $217.70   $217.70  
  Purchase #3 $166.28   3.867%   $172.71   $172.71   $172.70   $172.70  
  Purchase #4 $133.78   11.856%   $149.641   $149.64   $149.65   $149.60  
  Purchase #5 $179.92   13.742%   $204.6446   $204.64   $204.65   $204.60  
  Purchase #6 $120.62   3.810%   $125.2156   $125.22   $125.20   $125.20  
  Purchase #7 $185.51   12.514%   $208.7247   $208.72   $208.70   $208.70  
  7 purchase totals = $1,228.41       $1,344.8355   $1,344.83   $1,344.80   $1,344.70