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	$157.83	13.729%	$179.4985	$179.50	$179.50	$179.50
Purchase #2	$154.96	12.134%	$173.7628	$173.76	$173.75	$173.80
Purchase #3	$83.34	9.802%	$91.509	$91.51	$91.50	$91.50
Purchase #4	$151.85	6.789%	$162.1591	$162.16	$162.15	$162.20
Purchase #5	$164.56	11.353%	$183.2425	$183.24	$183.25	$183.20
Purchase #6	$194.63	13.855%	$221.596	$221.60	$221.60	$221.60
Purchase #7	$104.42	8.336%	$113.1245	$113.12	$113.10	$113.10
7 purchase totals =	$1,011.59		$1,124.8924	$1,124.89	$1,124.85	$1,124.90