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	$151.49	4.369%	$158.1086	$158.11	$158.10	$158.10
Purchase #2	$45.56	13.777%	$51.8368	$51.84	$51.85	$51.80
Purchase #3	$139.51	3.302%	$144.1166	$144.12	$144.10	$144.10
Purchase #4	$224.38	4.478%	$234.4277	$234.43	$234.45	$234.40
Purchase #5	$9.89	9.603%	$10.8397	$10.84	$10.85	$10.80
Purchase #6	$70.33	3.598%	$72.8605	$72.86	$72.85	$72.90
Purchase #7	$172.50	10.761%	$191.0627	$191.06	$191.05	$191.10
7 purchase totals =	$813.66		$863.2526	$863.26	$863.25	$863.20