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	$77.44	3.317%	$80.0087	$80.01	$80.00	$80.00
Purchase #2	$69.89	10.797%	$77.436	$77.44	$77.45	$77.40
Purchase #3	$108.62	8.541%	$117.8972	$117.90	$117.90	$117.90
Purchase #4	$97.30	11.501%	$108.4905	$108.49	$108.50	$108.50
Purchase #5	$152.82	3.205%	$157.7179	$157.72	$157.70	$157.70
Purchase #6	$40.65	11.756%	$45.4288	$45.43	$45.45	$45.40
Purchase #7	$89.98	5.109%	$94.5771	$94.58	$94.60	$94.60
7 purchase totals =	$636.70		$681.5562	$681.57	$681.60	$681.50