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	$26.26	12.531%	$29.5506	$29.55	$29.55	$29.60
Purchase #2	$227.33	12.220%	$255.1097	$255.11	$255.10	$255.10
Purchase #3	$42.70	6.258%	$45.3722	$45.37	$45.35	$45.40
Purchase #4	$239.76	5.837%	$253.7548	$253.75	$253.75	$253.80
Purchase #5	$193.52	13.677%	$219.9877	$219.99	$220.00	$220.00
Purchase #6	$143.71	11.869%	$160.7669	$160.77	$160.75	$160.80
Purchase #7	$89.55	11.463%	$99.8151	$99.82	$99.80	$99.80
7 purchase totals =	$962.83		$1,064.3570	$1,064.36	$1,064.30	$1,064.50