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	$106.46	4.729%	$111.4945	$111.49	$111.50	$111.50
Purchase #2	$24.29	9.396%	$26.5723	$26.57	$26.55	$26.60
Purchase #3	$33.48	6.463%	$35.6438	$35.64	$35.65	$35.60
Purchase #4	$93.74	6.516%	$99.8481	$99.85	$99.85	$99.80
Purchase #5	$37.30	9.607%	$40.8834	$40.88	$40.90	$40.90
Purchase #6	$70.51	3.407%	$72.9123	$72.91	$72.90	$72.90
Purchase #7	$139.42	10.111%	$153.5168	$153.52	$153.50	$153.50
7 purchase totals =	$505.20		$540.8712	$540.86	$540.85	$540.80