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	$56.96	4.166%	$59.333	$59.33	$59.35	$59.30
Purchase #2	$111.65	7.659%	$120.2013	$120.20	$120.20	$120.20
Purchase #3	$137.31	4.560%	$143.5713	$143.57	$143.55	$143.60
Purchase #4	$58.25	4.197%	$60.6948	$60.69	$60.70	$60.70
Purchase #5	$29.62	13.725%	$33.6853	$33.69	$33.70	$33.70
Purchase #6	$17.38	11.130%	$19.3144	$19.31	$19.30	$19.30
Purchase #7	$151.43	10.786%	$167.7632	$167.76	$167.75	$167.80
7 purchase totals =	$562.60		$604.5633	$604.55	$604.55	$604.60