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 $40.86   9.468%   $44.7286   $44.73   $44.75   $44.70  
  Purchase #2 $250.39   5.334%   $263.7458   $263.75   $263.75   $263.70  
  Purchase #3 $60.49   9.856%   $66.4519   $66.45   $66.45   $66.50  
  Purchase #4 $134.78   5.541%   $142.2482   $142.25   $142.25   $142.20  
  Purchase #5 $245.73   11.107%   $273.0232   $273.02   $273.00   $273.00  
  Purchase #6 $205.74   11.812%   $230.042   $230.04   $230.05   $230.00  
  Purchase #7 $13.88   5.825%   $14.6885   $14.69   $14.70   $14.70  
  7 purchase totals = $951.87       $1,034.9282   $1,034.93   $1,034.95   $1,034.80