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	$66.35	10.610%	$73.3897	$73.39	$73.40	$73.40
Purchase #2	$83.77	5.360%	$88.2601	$88.26	$88.25	$88.30
Purchase #3	$82.59	3.467%	$85.4534	$85.45	$85.45	$85.50
Purchase #4	$53.32	10.654%	$59.0007	$59.00	$59.00	$59.00
Purchase #5	$138.81	5.518%	$146.4695	$146.47	$146.45	$146.50
Purchase #6	$83.76	12.399%	$94.1454	$94.15	$94.15	$94.10
Purchase #7	$54.83	10.162%	$60.4018	$60.40	$60.40	$60.40
7 purchase totals =	$563.43		$607.1206	$607.12	$607.10	$607.20