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	$156.78	7.469%	$168.4899	$168.49	$168.50	$168.50
Purchase #2	$232.74	3.380%	$240.6066	$240.61	$240.60	$240.60
Purchase #3	$30.28	10.388%	$33.4255	$33.43	$33.45	$33.40
Purchase #4	$159.43	3.781%	$165.458	$165.46	$165.45	$165.50
Purchase #5	$98.77	10.569%	$109.209	$109.21	$109.20	$109.20
Purchase #6	$11.70	6.415%	$12.4506	$12.45	$12.45	$12.50
Purchase #7	$202.35	9.677%	$221.9314	$221.93	$221.95	$221.90
7 purchase totals =	$892.05		$951.5710	$951.58	$951.60	$951.60