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	$26.88	5.390%	$28.3288	$28.33	$28.35	$28.30
Purchase #2	$108.37	3.227%	$111.8671	$111.87	$111.85	$111.90
Purchase #3	$123.46	13.676%	$140.3444	$140.34	$140.35	$140.30
Purchase #4	$149.98	13.815%	$170.6997	$170.70	$170.70	$170.70
Purchase #5	$57.38	4.550%	$59.9908	$59.99	$60.00	$60.00
Purchase #6	$38.78	9.651%	$42.5227	$42.52	$42.50	$42.50
Purchase #7	$114.53	8.117%	$123.8264	$123.83	$123.85	$123.80
7 purchase totals =	$619.38		$677.5799	$677.58	$677.60	$677.50