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	$130.26	5.617%	$137.5767	$137.58	$137.60	$137.60
Purchase #2	$233.95	4.535%	$244.5596	$244.56	$244.55	$244.60
Purchase #3	$34.43	10.736%	$38.1264	$38.13	$38.15	$38.10
Purchase #4	$128.88	6.160%	$136.819	$136.82	$136.80	$136.80
Purchase #5	$141.46	3.748%	$146.7619	$146.76	$146.75	$146.80
Purchase #6	$83.86	12.846%	$94.6327	$94.63	$94.65	$94.60
Purchase #7	$185.26	10.157%	$204.0769	$204.08	$204.10	$204.10
7 purchase totals =	$938.10		$1,002.5532	$1,002.56	$1,002.60	$1,002.60