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	$85.61	6.168%	$90.8904	$90.89	$90.90	$90.90
Purchase #2	$244.43	9.700%	$268.1397	$268.14	$268.15	$268.10
Purchase #3	$59.80	10.853%	$66.2901	$66.29	$66.30	$66.30
Purchase #4	$193.72	12.371%	$217.6851	$217.69	$217.70	$217.70
Purchase #5	$159.43	8.536%	$173.0389	$173.04	$173.05	$173.00
Purchase #6	$173.85	12.265%	$195.1727	$195.17	$195.15	$195.20
Purchase #7	$94.47	3.262%	$97.5516	$97.55	$97.55	$97.60
7 purchase totals =	$1,011.31		$1,108.7685	$1,108.77	$1,108.80	$1,108.80