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 $52.41   10.608%   $57.9697   $57.97   $57.95   $58.00  
  Purchase #2 $133.83   9.693%   $146.8021   $146.80   $146.80   $146.80  
  Purchase #3 $46.40   6.266%   $49.3074   $49.31   $49.30   $49.30  
  Purchase #4 $83.34   11.241%   $92.7082   $92.71   $92.70   $92.70  
  Purchase #5 $231.49   4.427%   $241.7381   $241.74   $241.75   $241.70  
  Purchase #6 $30.31   6.338%   $32.231   $32.23   $32.25   $32.20  
  Purchase #7 $6.60   12.689%   $7.4375   $7.44   $7.45   $7.40  
  7 purchase totals = $584.38       $628.1940   $628.20   $628.20   $628.10