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	$33.80	11.808%	$37.7911	$37.79	$37.80	$37.80
Purchase #2	$224.95	7.322%	$241.4208	$241.42	$241.40	$241.40
Purchase #3	$249.40	7.184%	$267.3169	$267.32	$267.30	$267.30
Purchase #4	$197.43	7.314%	$211.87	$211.87	$211.85	$211.90
Purchase #5	$64.93	9.788%	$71.2853	$71.29	$71.30	$71.30
Purchase #6	$238.67	5.795%	$252.5009	$252.50	$252.50	$252.50
Purchase #7	$196.64	13.163%	$222.5237	$222.52	$222.50	$222.50
7 purchase totals =	$1,205.82		$1,304.7087	$1,304.71	$1,304.65	$1,304.70