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	$240.29	13.682%	$273.1665	$273.17	$273.15	$273.20
Purchase #2	$122.34	13.651%	$139.0406	$139.04	$139.05	$139.00
Purchase #3	$39.84	7.520%	$42.836	$42.84	$42.85	$42.80
Purchase #4	$49.44	7.322%	$53.06	$53.06	$53.05	$53.10
Purchase #5	$127.36	13.239%	$144.2212	$144.22	$144.20	$144.20
Purchase #6	$207.79	7.537%	$223.4511	$223.45	$223.45	$223.50
Purchase #7	$210.53	12.407%	$236.6505	$236.65	$236.65	$236.70
7 purchase totals =	$997.59		$1,112.4259	$1,112.43	$1,112.40	$1,112.50