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	$85.76	3.263%	$88.5583	$88.56	$88.55	$88.60
Purchase #2	$106.84	7.538%	$114.8936	$114.89	$114.90	$114.90
Purchase #3	$183.62	11.784%	$205.2578	$205.26	$205.25	$205.30
Purchase #4	$30.82	9.444%	$33.7306	$33.73	$33.75	$33.70
Purchase #5	$85.69	11.677%	$95.696	$95.70	$95.70	$95.70
Purchase #6	$54.78	10.451%	$60.5051	$60.51	$60.50	$60.50
Purchase #7	$176.57	13.603%	$200.5888	$200.59	$200.60	$200.60
7 purchase totals =	$724.08		$799.2302	$799.24	$799.25	$799.30