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	$27.42	12.705%	$30.9037	$30.90	$30.90	$30.90
Purchase #2	$24.70	11.653%	$27.5783	$27.58	$27.60	$27.60
Purchase #3	$188.42	12.714%	$212.3757	$212.38	$212.40	$212.40
Purchase #4	$56.77	13.282%	$64.3102	$64.31	$64.30	$64.30
Purchase #5	$52.73	12.869%	$59.5158	$59.52	$59.50	$59.50
Purchase #6	$59.75	5.194%	$62.8534	$62.85	$62.85	$62.90
Purchase #7	$133.88	8.638%	$145.4446	$145.44	$145.45	$145.40
7 purchase totals =	$543.67		$602.9817	$602.98	$603.00	$603.00