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 $55.44   12.201%   $62.2042   $62.20   $62.20   $62.20  
  Purchase #2 $58.95   5.346%   $62.1015   $62.10   $62.10   $62.10  
  Purchase #3 $31.47   9.295%   $34.3951   $34.40   $34.40   $34.40  
  Purchase #4 $30.36   8.472%   $32.9321   $32.93   $32.95   $32.90  
  Purchase #5 $118.97   6.160%   $126.2986   $126.30   $126.30   $126.30  
  Purchase #6 $55.89   4.810%   $58.5783   $58.58   $58.60   $58.60  
  Purchase #7 $184.62   6.427%   $196.4855   $196.49   $196.50   $196.50  
  7 purchase totals = $535.70       $572.9953   $573.00   $573.05   $573.00