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	$157.76	6.836%	$168.5445	$168.54	$168.55	$168.50
Purchase #2	$172.81	8.114%	$186.8318	$186.83	$186.85	$186.80
Purchase #3	$243.41	6.817%	$260.0033	$260.00	$260.00	$260.00
Purchase #4	$148.74	11.406%	$165.7053	$165.71	$165.70	$165.70
Purchase #5	$126.72	10.865%	$140.4881	$140.49	$140.50	$140.50
Purchase #6	$141.33	3.577%	$146.3854	$146.39	$146.40	$146.40
Purchase #7	$50.26	12.498%	$56.5415	$56.54	$56.55	$56.50
7 purchase totals =	$1,041.03		$1,124.4999	$1,124.50	$1,124.55	$1,124.40