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	$100.51	3.195%	$103.7213	$103.72	$103.70	$103.70
Purchase #2	$64.95	12.134%	$72.831	$72.83	$72.85	$72.80
Purchase #3	$20.46	4.157%	$21.3105	$21.31	$21.30	$21.30
Purchase #4	$136.91	3.479%	$141.6731	$141.67	$141.65	$141.70
Purchase #5	$85.45	10.789%	$94.6692	$94.67	$94.65	$94.70
Purchase #6	$9.85	12.374%	$11.0688	$11.07	$11.05	$11.10
Purchase #7	$83.66	9.386%	$91.5123	$91.51	$91.50	$91.50
7 purchase totals =	$501.79		$536.7862	$536.78	$536.70	$536.80