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	$37.91	12.153%	$42.5172	$42.52	$42.50	$42.50
Purchase #2	$12.34	7.257%	$13.2355	$13.24	$13.25	$13.20
Purchase #3	$176.78	3.499%	$182.9655	$182.97	$182.95	$183.00
Purchase #4	$171.88	12.740%	$193.7775	$193.78	$193.80	$193.80
Purchase #5	$138.53	4.345%	$144.5491	$144.55	$144.55	$144.50
Purchase #6	$88.62	13.389%	$100.4853	$100.49	$100.50	$100.50
Purchase #7	$54.97	3.594%	$56.9456	$56.95	$56.95	$56.90
7 purchase totals =	$681.03		$734.4757	$734.50	$734.50	$734.40