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	$86.79	4.214%	$90.4473	$90.45	$90.45	$90.40
Purchase #2	$59.35	3.341%	$61.3329	$61.33	$61.35	$61.30
Purchase #3	$16.67	10.304%	$18.3877	$18.39	$18.40	$18.40
Purchase #4	$205.33	7.202%	$220.1179	$220.12	$220.10	$220.10
Purchase #5	$107.76	13.678%	$122.4994	$122.50	$122.50	$122.50
Purchase #6	$200.47	4.119%	$208.7274	$208.73	$208.75	$208.70
Purchase #7	$221.32	3.829%	$229.7943	$229.79	$229.80	$229.80
7 purchase totals =	$897.69		$951.3069	$951.31	$951.35	$951.20