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	$152.88	8.812%	$166.3518	$166.35	$166.35	$166.40
Purchase #2	$231.71	13.462%	$262.9028	$262.90	$262.90	$262.90
Purchase #3	$141.29	11.526%	$157.5751	$157.58	$157.60	$157.60
Purchase #4	$141.72	10.240%	$156.2321	$156.23	$156.25	$156.20
Purchase #5	$191.77	9.314%	$209.6315	$209.63	$209.65	$209.60
Purchase #6	$94.30	6.299%	$100.24	$100.24	$100.25	$100.20
Purchase #7	$79.96	13.195%	$90.5107	$90.51	$90.50	$90.50
7 purchase totals =	$1,033.63		$1,143.4440	$1,143.44	$1,143.50	$1,143.40