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	$240.26	6.307%	$255.4132	$255.41	$255.40	$255.40
Purchase #2	$45.96	7.241%	$49.288	$49.29	$49.30	$49.30
Purchase #3	$47.45	13.574%	$53.8909	$53.89	$53.90	$53.90
Purchase #4	$109.27	11.850%	$122.2185	$122.22	$122.20	$122.20
Purchase #5	$44.76	13.154%	$50.6477	$50.65	$50.65	$50.60
Purchase #6	$139.87	7.297%	$150.0763	$150.08	$150.10	$150.10
Purchase #7	$29.77	10.155%	$32.7931	$32.79	$32.80	$32.80
7 purchase totals =	$657.34		$714.3277	$714.33	$714.35	$714.30