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	$65.26	10.139%	$71.8767	$71.88	$71.90	$71.90
Purchase #2	$34.94	10.191%	$38.5007	$38.50	$38.50	$38.50
Purchase #3	$207.68	13.298%	$235.2973	$235.30	$235.30	$235.30
Purchase #4	$228.61	9.571%	$250.4903	$250.49	$250.50	$250.50
Purchase #5	$38.61	4.873%	$40.4915	$40.49	$40.50	$40.50
Purchase #6	$85.98	9.477%	$94.1283	$94.13	$94.15	$94.10
Purchase #7	$30.97	5.802%	$32.7669	$32.77	$32.75	$32.80
7 purchase totals =	$692.05		$763.5517	$763.56	$763.60	$763.60