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	$54.67	12.823%	$61.6803	$61.68	$61.70	$61.70
Purchase #2	$152.80	4.389%	$159.5064	$159.51	$159.50	$159.50
Purchase #3	$26.68	6.654%	$28.4553	$28.46	$28.45	$28.50
Purchase #4	$100.37	9.822%	$110.2283	$110.23	$110.25	$110.20
Purchase #5	$170.72	8.585%	$185.3763	$185.38	$185.40	$185.40
Purchase #6	$74.32	11.260%	$82.6884	$82.69	$82.70	$82.70
Purchase #7	$143.27	8.703%	$155.7388	$155.74	$155.75	$155.70
7 purchase totals =	$722.83		$783.6738	$783.69	$783.75	$783.70