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	$53.70	13.317%	$60.8512	$60.85	$60.85	$60.90
Purchase #2	$217.55	6.523%	$231.7408	$231.74	$231.75	$231.70
Purchase #3	$182.64	4.410%	$190.6944	$190.69	$190.70	$190.70
Purchase #4	$69.84	3.465%	$72.26	$72.26	$72.25	$72.30
Purchase #5	$90.49	11.700%	$101.0773	$101.08	$101.10	$101.10
Purchase #6	$60.25	9.530%	$65.9918	$65.99	$66.00	$66.00
Purchase #7	$103.63	7.698%	$111.6074	$111.61	$111.60	$111.60
7 purchase totals =	$778.10		$834.2229	$834.22	$834.25	$834.30