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	$113.27	13.628%	$128.7064	$128.71	$128.70	$128.70
Purchase #2	$150.71	3.190%	$155.5176	$155.52	$155.50	$155.50
Purchase #3	$57.42	8.740%	$62.4385	$62.44	$62.45	$62.40
Purchase #4	$250.93	13.785%	$285.5207	$285.52	$285.50	$285.50
Purchase #5	$130.37	12.257%	$146.3495	$146.35	$146.35	$146.30
Purchase #6	$246.32	11.747%	$275.2552	$275.26	$275.25	$275.30
Purchase #7	$133.97	8.597%	$145.4874	$145.49	$145.50	$145.50
7 purchase totals =	$1,082.99		$1,199.2753	$1,199.29	$1,199.25	$1,199.20