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	$72.66	7.507%	$78.1146	$78.11	$78.10	$78.10
Purchase #2	$156.41	7.613%	$168.3175	$168.32	$168.30	$168.30
Purchase #3	$52.78	10.599%	$58.3742	$58.37	$58.35	$58.40
Purchase #4	$100.34	4.203%	$104.5573	$104.56	$104.55	$104.60
Purchase #5	$10.77	8.232%	$11.6566	$11.66	$11.65	$11.70
Purchase #6	$94.66	4.810%	$99.2131	$99.21	$99.20	$99.20
Purchase #7	$152.75	3.102%	$157.4883	$157.49	$157.50	$157.50
7 purchase totals =	$640.37		$677.7216	$677.72	$677.65	$677.80