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	$152.79	11.237%	$169.959	$169.96	$169.95	$170.00
Purchase #2	$91.81	9.552%	$100.5797	$100.58	$100.60	$100.60
Purchase #3	$185.29	7.499%	$199.1849	$199.18	$199.20	$199.20
Purchase #4	$158.89	12.543%	$178.8196	$178.82	$178.80	$178.80
Purchase #5	$126.34	12.261%	$141.8305	$141.83	$141.85	$141.80
Purchase #6	$80.51	7.331%	$86.4122	$86.41	$86.40	$86.40
Purchase #7	$93.84	13.805%	$106.7946	$106.79	$106.80	$106.80
7 purchase totals =	$889.47		$983.5805	$983.57	$983.60	$983.60