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	$160.52	3.727%	$166.5026	$166.50	$166.50	$166.50
Purchase #2	$208.44	10.350%	$230.0135	$230.01	$230.00	$230.00
Purchase #3	$91.76	9.231%	$100.2304	$100.23	$100.25	$100.20
Purchase #4	$42.66	11.830%	$47.7067	$47.71	$47.70	$47.70
Purchase #5	$169.75	12.586%	$191.1147	$191.11	$191.10	$191.10
Purchase #6	$130.93	10.595%	$144.802	$144.80	$144.80	$144.80
Purchase #7	$166.39	4.725%	$174.2519	$174.25	$174.25	$174.30
7 purchase totals =	$970.45		$1,054.6218	$1,054.61	$1,054.60	$1,054.60