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	$144.26	6.167%	$153.1565	$153.16	$153.15	$153.20
Purchase #2	$36.70	4.359%	$38.2998	$38.30	$38.30	$38.30
Purchase #3	$74.79	4.539%	$78.1847	$78.18	$78.20	$78.20
Purchase #4	$235.78	6.105%	$250.1744	$250.17	$250.15	$250.20
Purchase #5	$29.76	6.318%	$31.6402	$31.64	$31.65	$31.60
Purchase #6	$28.72	10.812%	$31.8252	$31.83	$31.85	$31.80
Purchase #7	$188.71	6.232%	$200.4704	$200.47	$200.45	$200.50
7 purchase totals =	$738.72		$783.7512	$783.75	$783.75	$783.80