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	$139.69	6.253%	$148.4248	$148.42	$148.40	$148.40
Purchase #2	$158.30	11.105%	$175.8792	$175.88	$175.90	$175.90
Purchase #3	$123.70	3.465%	$127.9862	$127.99	$128.00	$128.00
Purchase #4	$25.85	10.108%	$28.4629	$28.46	$28.45	$28.50
Purchase #5	$22.26	10.369%	$24.5681	$24.57	$24.55	$24.60
Purchase #6	$242.45	11.863%	$271.2118	$271.21	$271.20	$271.20
Purchase #7	$81.58	10.297%	$89.9803	$89.98	$90.00	$90.00
7 purchase totals =	$793.83		$866.5133	$866.51	$866.50	$866.60