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	$156.51	13.819%	$178.1381	$178.14	$178.15	$178.10
Purchase #2	$146.41	10.369%	$161.5913	$161.59	$161.60	$161.60
Purchase #3	$168.85	13.474%	$191.6008	$191.60	$191.60	$191.60
Purchase #4	$58.36	12.822%	$65.8429	$65.84	$65.85	$65.80
Purchase #5	$47.28	12.505%	$53.1924	$53.19	$53.20	$53.20
Purchase #6	$69.35	3.122%	$71.5151	$71.52	$71.50	$71.50
Purchase #7	$59.91	8.693%	$65.118	$65.12	$65.10	$65.10
7 purchase totals =	$706.67		$786.9986	$787.00	$787.00	$786.90