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	$40.83	5.613%	$43.1218	$43.12	$43.10	$43.10
Purchase #2	$144.27	4.456%	$150.6987	$150.70	$150.70	$150.70
Purchase #3	$82.56	3.206%	$85.2069	$85.21	$85.20	$85.20
Purchase #4	$56.75	13.181%	$64.2302	$64.23	$64.25	$64.20
Purchase #5	$101.64	4.820%	$106.539	$106.54	$106.55	$106.50
Purchase #6	$140.78	3.366%	$145.5187	$145.52	$145.50	$145.50
Purchase #7	$37.41	9.400%	$40.9265	$40.93	$40.95	$40.90
7 purchase totals =	$604.24		$636.2418	$636.25	$636.25	$636.10