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	$27.90	4.600%	$29.1834	$29.18	$29.20	$29.20
Purchase #2	$189.44	5.316%	$199.5106	$199.51	$199.50	$199.50
Purchase #3	$233.36	4.501%	$243.8635	$243.86	$243.85	$243.90
Purchase #4	$58.71	3.205%	$60.5917	$60.59	$60.60	$60.60
Purchase #5	$134.89	4.852%	$141.4349	$141.43	$141.45	$141.40
Purchase #6	$102.61	13.186%	$116.1402	$116.14	$116.15	$116.10
Purchase #7	$34.55	8.446%	$37.4681	$37.47	$37.45	$37.50
7 purchase totals =	$781.46		$828.1924	$828.18	$828.20	$828.20