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	$11.92	4.825%	$12.4951	$12.50	$12.50	$12.50
Purchase #2	$37.78	11.371%	$42.076	$42.08	$42.10	$42.10
Purchase #3	$249.89	8.121%	$270.1836	$270.18	$270.20	$270.20
Purchase #4	$7.45	5.780%	$7.8806	$7.88	$7.90	$7.90
Purchase #5	$52.44	8.546%	$56.9215	$56.92	$56.90	$56.90
Purchase #6	$159.87	3.259%	$165.0802	$165.08	$165.10	$165.10
Purchase #7	$83.87	13.732%	$95.387	$95.39	$95.40	$95.40
7 purchase totals =	$603.22		$650.0240	$650.03	$650.10	$650.10