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	$72.89	13.323%	$82.6011	$82.60	$82.60	$82.60
Purchase #2	$46.31	4.412%	$48.3532	$48.35	$48.35	$48.40
Purchase #3	$142.86	4.218%	$148.8858	$148.89	$148.90	$148.90
Purchase #4	$49.73	6.815%	$53.1191	$53.12	$53.10	$53.10
Purchase #5	$49.73	5.125%	$52.2787	$52.28	$52.30	$52.30
Purchase #6	$54.39	7.527%	$58.4839	$58.48	$58.50	$58.50
Purchase #7	$161.55	7.733%	$174.0427	$174.04	$174.05	$174.00
7 purchase totals =	$577.46		$617.7645	$617.76	$617.80	$617.80