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	$97.55	12.131%	$109.3838	$109.38	$109.40	$109.40
Purchase #2	$70.32	11.567%	$78.4539	$78.45	$78.45	$78.50
Purchase #3	$166.72	8.589%	$181.0396	$181.04	$181.05	$181.00
Purchase #4	$74.92	3.236%	$77.3444	$77.34	$77.35	$77.30
Purchase #5	$211.71	5.753%	$223.8897	$223.89	$223.90	$223.90
Purchase #6	$112.43	10.388%	$124.1092	$124.11	$124.10	$124.10
Purchase #7	$186.61	4.222%	$194.4887	$194.49	$194.50	$194.50
7 purchase totals =	$920.26		$988.7093	$988.70	$988.75	$988.70