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 $66.67   10.318%   $73.549   $73.55   $73.55   $73.50  
  Purchase #2 $131.42   6.329%   $139.7376   $139.74   $139.75   $139.70  
  Purchase #3 $51.32   11.733%   $57.3414   $57.34   $57.35   $57.30  
  Purchase #4 $200.50   7.132%   $214.7997   $214.80   $214.80   $214.80  
  Purchase #5 $219.44   7.806%   $236.5695   $236.57   $236.55   $236.60  
  Purchase #6 $33.87   4.842%   $35.51   $35.51   $35.50   $35.50  
  Purchase #7 $14.83   7.174%   $15.8939   $15.89   $15.90   $15.90  
  7 purchase totals = $718.05       $773.4011   $773.40   $773.40   $773.30