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	$152.39	3.795%	$158.1732	$158.17	$158.15	$158.20
Purchase #2	$96.44	9.274%	$105.3838	$105.38	$105.40	$105.40
Purchase #3	$238.30	9.436%	$260.786	$260.79	$260.80	$260.80
Purchase #4	$129.50	7.678%	$139.443	$139.44	$139.45	$139.40
Purchase #5	$190.80	13.583%	$216.7164	$216.72	$216.70	$216.70
Purchase #6	$146.87	7.240%	$157.5034	$157.50	$157.50	$157.50
Purchase #7	$39.48	8.305%	$42.7588	$42.76	$42.75	$42.80
7 purchase totals =	$993.78		$1,080.7646	$1,080.76	$1,080.75	$1,080.80