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	$165.52	3.227%	$170.8613	$170.86	$170.85	$170.90
Purchase #2	$18.80	8.486%	$20.3954	$20.40	$20.40	$20.40
Purchase #3	$117.43	7.586%	$126.3382	$126.34	$126.35	$126.30
Purchase #4	$37.73	11.750%	$42.1633	$42.16	$42.15	$42.20
Purchase #5	$170.41	12.607%	$191.8936	$191.89	$191.90	$191.90
Purchase #6	$11.55	7.395%	$12.4041	$12.40	$12.40	$12.40
Purchase #7	$249.40	12.104%	$279.5874	$279.59	$279.60	$279.60
7 purchase totals =	$770.84		$843.6433	$843.64	$843.65	$843.70