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	$243.56	6.691%	$259.8566	$259.86	$259.85	$259.90
Purchase #2	$83.86	6.235%	$89.0887	$89.09	$89.10	$89.10
Purchase #3	$234.47	8.435%	$254.2475	$254.25	$254.25	$254.20
Purchase #4	$209.94	6.413%	$223.4035	$223.40	$223.40	$223.40
Purchase #5	$100.54	11.172%	$111.7723	$111.77	$111.75	$111.80
Purchase #6	$118.59	6.347%	$126.1169	$126.12	$126.10	$126.10
Purchase #7	$149.65	7.523%	$160.9082	$160.91	$160.90	$160.90
7 purchase totals =	$1,140.61		$1,225.3937	$1,225.40	$1,225.35	$1,225.40