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	$111.31	4.861%	$116.7208	$116.72	$116.70	$116.70
Purchase #2	$126.50	12.599%	$142.4377	$142.44	$142.45	$142.40
Purchase #3	$65.37	10.113%	$71.9809	$71.98	$72.00	$72.00
Purchase #4	$86.65	9.555%	$94.9294	$94.93	$94.95	$94.90
Purchase #5	$12.36	8.467%	$13.4065	$13.41	$13.40	$13.40
Purchase #6	$38.27	3.454%	$39.5918	$39.59	$39.60	$39.60
Purchase #7	$181.91	9.559%	$199.2988	$199.30	$199.30	$199.30
7 purchase totals =	$622.37		$678.3659	$678.37	$678.40	$678.30