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	$239.29	5.184%	$251.6948	$251.69	$251.70	$251.70
Purchase #2	$21.61	8.516%	$23.4503	$23.45	$23.45	$23.50
Purchase #3	$108.44	3.123%	$111.8266	$111.83	$111.85	$111.80
Purchase #4	$171.78	10.378%	$189.6073	$189.61	$189.60	$189.60
Purchase #5	$80.69	10.456%	$89.1269	$89.13	$89.15	$89.10
Purchase #6	$175.54	11.227%	$195.2479	$195.25	$195.25	$195.20
Purchase #7	$53.82	6.122%	$57.1149	$57.11	$57.10	$57.10
7 purchase totals =	$851.17		$918.0687	$918.07	$918.10	$918.00