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	$28.46	5.798%	$30.1101	$30.11	$30.10	$30.10
Purchase #2	$158.43	10.639%	$175.2854	$175.29	$175.30	$175.30
Purchase #3	$40.74	12.383%	$45.7848	$45.78	$45.80	$45.80
Purchase #4	$37.52	13.518%	$42.592	$42.59	$42.60	$42.60
Purchase #5	$15.58	4.794%	$16.3269	$16.33	$16.35	$16.30
Purchase #6	$83.64	6.750%	$89.2857	$89.29	$89.30	$89.30
Purchase #7	$172.48	7.756%	$185.8575	$185.86	$185.85	$185.90
7 purchase totals =	$536.85		$585.2424	$585.25	$585.30	$585.30