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	$228.53	9.476%	$250.1855	$250.19	$250.20	$250.20
Purchase #2	$120.54	8.353%	$130.6087	$130.61	$130.60	$130.60
Purchase #3	$99.82	12.342%	$112.1398	$112.14	$112.15	$112.10
Purchase #4	$157.52	6.740%	$168.1368	$168.14	$168.15	$168.10
Purchase #5	$34.39	13.777%	$39.1279	$39.13	$39.15	$39.10
Purchase #6	$60.52	7.320%	$64.9501	$64.95	$64.95	$65.00
Purchase #7	$92.27	6.389%	$98.1651	$98.17	$98.15	$98.20
7 purchase totals =	$793.59		$863.3139	$863.33	$863.35	$863.30