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	$95.72	3.631%	$99.1956	$99.20	$99.20	$99.20
Purchase #2	$122.72	3.633%	$127.1784	$127.18	$127.20	$127.20
Purchase #3	$92.73	12.635%	$104.4464	$104.45	$104.45	$104.40
Purchase #4	$131.35	4.364%	$137.0821	$137.08	$137.10	$137.10
Purchase #5	$187.54	4.672%	$196.3019	$196.30	$196.30	$196.30
Purchase #6	$137.34	4.191%	$143.0959	$143.10	$143.10	$143.10
Purchase #7	$162.48	13.636%	$184.6358	$184.64	$184.65	$184.60
7 purchase totals =	$929.88		$991.9361	$991.95	$992.00	$991.90