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	$20.28	5.119%	$21.3181	$21.32	$21.30	$21.30
Purchase #2	$101.74	12.519%	$114.4768	$114.48	$114.50	$114.50
Purchase #3	$80.70	7.731%	$86.9389	$86.94	$86.95	$86.90
Purchase #4	$212.25	10.135%	$233.7615	$233.76	$233.75	$233.80
Purchase #5	$157.64	4.778%	$165.172	$165.17	$165.15	$165.20
Purchase #6	$95.34	8.396%	$103.3447	$103.34	$103.35	$103.30
Purchase #7	$163.67	3.144%	$168.8158	$168.82	$168.80	$168.80
7 purchase totals =	$831.62		$893.8278	$893.83	$893.80	$893.80