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	$89.78	10.604%	$99.3003	$99.30	$99.30	$99.30
Purchase #2	$93.40	6.714%	$99.6709	$99.67	$99.65	$99.70
Purchase #3	$20.49	10.344%	$22.6095	$22.61	$22.60	$22.60
Purchase #4	$195.74	7.546%	$210.5105	$210.51	$210.50	$210.50
Purchase #5	$48.72	3.862%	$50.6016	$50.60	$50.60	$50.60
Purchase #6	$170.77	3.637%	$176.9809	$176.98	$177.00	$177.00
Purchase #7	$55.54	6.780%	$59.3056	$59.31	$59.30	$59.30
7 purchase totals =	$674.44		$718.9793	$718.98	$718.95	$719.00