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	$84.38	7.280%	$90.5229	$90.52	$90.50	$90.50
Purchase #2	$244.80	10.840%	$271.3363	$271.34	$271.35	$271.30
Purchase #3	$134.73	7.195%	$144.4238	$144.42	$144.40	$144.40
Purchase #4	$83.77	5.494%	$88.3723	$88.37	$88.35	$88.40
Purchase #5	$163.32	10.173%	$179.9345	$179.93	$179.95	$179.90
Purchase #6	$15.99	11.721%	$17.8642	$17.86	$17.85	$17.90
Purchase #7	$32.30	4.460%	$33.7406	$33.74	$33.75	$33.70
7 purchase totals =	$759.29		$826.1946	$826.18	$826.15	$826.10