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 $57.84   4.331%   $60.3451   $60.35   $60.35   $60.30  
  Purchase #2 $195.45   6.678%   $208.5022   $208.50   $208.50   $208.50  
  Purchase #3 $125.80   5.739%   $133.0197   $133.02   $133.00   $133.00  
  Purchase #4 $51.43   12.178%   $57.6931   $57.69   $57.70   $57.70  
  Purchase #5 $242.35   7.359%   $260.1845   $260.18   $260.20   $260.20  
  Purchase #6 $203.87   11.224%   $226.7524   $226.75   $226.75   $226.80  
  Purchase #7 $79.43   5.443%   $83.7534   $83.75   $83.75   $83.80  
  7 purchase totals = $956.17       $1,030.2504   $1,030.24   $1,030.25   $1,030.30