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	$237.27	5.755%	$250.9249	$250.92	$250.90	$250.90
Purchase #2	$71.73	13.863%	$81.6739	$81.67	$81.65	$81.70
Purchase #3	$92.47	7.627%	$99.5227	$99.52	$99.50	$99.50
Purchase #4	$35.25	11.392%	$39.2657	$39.27	$39.25	$39.30
Purchase #5	$110.49	5.528%	$116.5979	$116.60	$116.60	$116.60
Purchase #6	$129.82	7.456%	$139.4994	$139.50	$139.50	$139.50
Purchase #7	$57.39	4.532%	$59.9909	$59.99	$60.00	$60.00
7 purchase totals =	$734.42		$787.4754	$787.47	$787.40	$787.50