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	$211.72	12.587%	$238.3692	$238.37	$238.35	$238.40
Purchase #2	$81.49	5.328%	$85.8318	$85.83	$85.85	$85.80
Purchase #3	$218.36	10.148%	$240.5192	$240.52	$240.50	$240.50
Purchase #4	$138.54	13.599%	$157.3801	$157.38	$157.40	$157.40
Purchase #5	$137.29	12.413%	$154.3318	$154.33	$154.35	$154.30
Purchase #6	$28.66	12.205%	$32.158	$32.16	$32.15	$32.20
Purchase #7	$121.42	8.699%	$131.9823	$131.98	$132.00	$132.00
7 purchase totals =	$937.48		$1,040.5724	$1,040.57	$1,040.60	$1,040.60