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	$136.68	7.156%	$146.4608	$146.46	$146.45	$146.50
Purchase #2	$128.30	12.533%	$144.3798	$144.38	$144.40	$144.40
Purchase #3	$233.31	4.527%	$243.8719	$243.87	$243.85	$243.90
Purchase #4	$34.48	3.678%	$35.7482	$35.75	$35.75	$35.70
Purchase #5	$15.87	7.527%	$17.0645	$17.06	$17.05	$17.10
Purchase #6	$212.88	11.580%	$237.5315	$237.53	$237.55	$237.50
Purchase #7	$71.88	9.118%	$78.434	$78.43	$78.45	$78.40
7 purchase totals =	$833.40		$903.4907	$903.48	$903.50	$903.50