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	$38.52	9.561%	$42.2029	$42.20	$42.20	$42.20
Purchase #2	$93.83	6.680%	$100.0978	$100.10	$100.10	$100.10
Purchase #3	$61.88	3.631%	$64.1269	$64.13	$64.15	$64.10
Purchase #4	$61.59	6.130%	$65.3655	$65.37	$65.35	$65.40
Purchase #5	$160.79	11.336%	$179.0172	$179.02	$179.00	$179.00
Purchase #6	$37.31	6.596%	$39.771	$39.77	$39.75	$39.80
Purchase #7	$99.51	12.106%	$111.5567	$111.56	$111.55	$111.60
7 purchase totals =	$553.43		$602.1380	$602.15	$602.10	$602.20