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	$34.56	7.838%	$37.2688	$37.27	$37.25	$37.30
Purchase #2	$21.31	5.598%	$22.5029	$22.50	$22.50	$22.50
Purchase #3	$10.25	3.190%	$10.577	$10.58	$10.60	$10.60
Purchase #4	$136.73	6.569%	$145.7118	$145.71	$145.70	$145.70
Purchase #5	$171.79	11.584%	$191.6902	$191.69	$191.70	$191.70
Purchase #6	$143.77	4.404%	$150.1016	$150.10	$150.10	$150.10
Purchase #7	$83.78	7.288%	$89.8859	$89.89	$89.90	$89.90
7 purchase totals =	$602.19		$647.7382	$647.74	$647.75	$647.80