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	$25.52	7.307%	$27.3847	$27.38	$27.40	$27.40
Purchase #2	$127.77	10.210%	$140.8153	$140.82	$140.80	$140.80
Purchase #3	$23.64	5.330%	$24.9	$24.90	$24.90	$24.90
Purchase #4	$226.72	12.386%	$254.8015	$254.80	$254.80	$254.80
Purchase #5	$145.42	13.586%	$165.1768	$165.18	$165.20	$165.20
Purchase #6	$36.47	9.258%	$39.8464	$39.85	$39.85	$39.80
Purchase #7	$60.77	11.196%	$67.5738	$67.57	$67.55	$67.60
7 purchase totals =	$646.31		$720.4985	$720.50	$720.50	$720.50