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	$45.33	5.719%	$47.9224	$47.92	$47.90	$47.90
Purchase #2	$227.82	11.451%	$253.9077	$253.91	$253.90	$253.90
Purchase #3	$96.49	5.361%	$101.6628	$101.66	$101.65	$101.70
Purchase #4	$107.74	8.372%	$116.76	$116.76	$116.75	$116.80
Purchase #5	$247.59	6.759%	$264.3246	$264.32	$264.30	$264.30
Purchase #6	$61.47	7.781%	$66.253	$66.25	$66.25	$66.30
Purchase #7	$80.68	10.657%	$89.2781	$89.28	$89.30	$89.30
7 purchase totals =	$867.12		$940.1086	$940.10	$940.05	$940.20