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	$57.40	6.852%	$61.333	$61.33	$61.35	$61.30
Purchase #2	$158.59	13.374%	$179.7998	$179.80	$179.80	$179.80
Purchase #3	$234.67	4.778%	$245.8825	$245.88	$245.90	$245.90
Purchase #4	$138.52	8.310%	$150.031	$150.03	$150.05	$150.00
Purchase #5	$57.87	4.322%	$60.3711	$60.37	$60.35	$60.40
Purchase #6	$39.92	4.244%	$41.6142	$41.61	$41.60	$41.60
Purchase #7	$75.79	7.262%	$81.2939	$81.29	$81.30	$81.30
7 purchase totals =	$762.76		$820.3255	$820.31	$820.35	$820.30