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	$73.46	13.275%	$83.2118	$83.21	$83.20	$83.20
Purchase #2	$88.67	13.532%	$100.6688	$100.67	$100.65	$100.70
Purchase #3	$200.65	10.472%	$221.6621	$221.66	$221.65	$221.70
Purchase #4	$185.52	3.121%	$191.3101	$191.31	$191.30	$191.30
Purchase #5	$250.94	4.783%	$262.9425	$262.94	$262.95	$262.90
Purchase #6	$66.31	5.170%	$69.7382	$69.74	$69.75	$69.70
Purchase #7	$12.85	3.754%	$13.3324	$13.33	$13.35	$13.30
7 purchase totals =	$878.40		$942.8659	$942.86	$942.85	$942.80