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	$154.69	10.854%	$171.4801	$171.48	$171.50	$171.50
Purchase #2	$75.79	8.580%	$82.2928	$82.29	$82.30	$82.30
Purchase #3	$244.49	13.767%	$278.1489	$278.15	$278.15	$278.10
Purchase #4	$30.42	6.248%	$32.3206	$32.32	$32.30	$32.30
Purchase #5	$114.72	3.141%	$118.3234	$118.32	$118.30	$118.30
Purchase #6	$162.94	6.562%	$173.6321	$173.63	$173.65	$173.60
Purchase #7	$127.50	3.333%	$131.7496	$131.75	$131.75	$131.70
7 purchase totals =	$910.55		$987.9475	$987.94	$987.95	$987.80