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	$58.52	3.539%	$60.591	$60.59	$60.60	$60.60
Purchase #2	$129.56	11.367%	$144.2871	$144.29	$144.30	$144.30
Purchase #3	$187.96	13.745%	$213.7951	$213.80	$213.80	$213.80
Purchase #4	$223.97	6.390%	$238.2817	$238.28	$238.30	$238.30
Purchase #5	$28.96	9.571%	$31.7318	$31.73	$31.75	$31.70
Purchase #6	$86.49	4.121%	$90.0543	$90.05	$90.05	$90.10
Purchase #7	$46.79	8.251%	$50.6506	$50.65	$50.65	$50.70
7 purchase totals =	$762.25		$829.3916	$829.39	$829.45	$829.50