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	$104.55	6.572%	$111.421	$111.42	$111.40	$111.40
Purchase #2	$47.82	6.160%	$50.7657	$50.77	$50.75	$50.80
Purchase #3	$30.62	6.341%	$32.5616	$32.56	$32.55	$32.60
Purchase #4	$121.98	7.851%	$131.5566	$131.56	$131.55	$131.60
Purchase #5	$204.98	12.525%	$230.6537	$230.65	$230.65	$230.70
Purchase #6	$20.72	4.396%	$21.6309	$21.63	$21.65	$21.60
Purchase #7	$188.98	12.592%	$212.7764	$212.78	$212.80	$212.80
7 purchase totals =	$719.65		$791.3659	$791.37	$791.35	$791.50