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	$114.81	3.135%	$118.4093	$118.41	$118.40	$118.40
Purchase #2	$240.40	12.266%	$269.8875	$269.89	$269.90	$269.90
Purchase #3	$102.73	8.396%	$111.3552	$111.36	$111.35	$111.40
Purchase #4	$49.53	9.721%	$54.3448	$54.34	$54.35	$54.30
Purchase #5	$225.49	8.329%	$244.2711	$244.27	$244.25	$244.30
Purchase #6	$126.45	8.733%	$137.4929	$137.49	$137.50	$137.50
Purchase #7	$25.72	9.305%	$28.1132	$28.11	$28.10	$28.10
7 purchase totals =	$885.13		$963.8740	$963.87	$963.85	$963.90