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	$156.90	7.611%	$168.8417	$168.84	$168.85	$168.80
Purchase #2	$172.59	4.721%	$180.738	$180.74	$180.75	$180.70
Purchase #3	$173.93	3.725%	$180.4089	$180.41	$180.40	$180.40
Purchase #4	$211.48	10.278%	$233.2159	$233.22	$233.20	$233.20
Purchase #5	$94.63	6.429%	$100.7138	$100.71	$100.70	$100.70
Purchase #6	$215.32	3.435%	$222.7162	$222.72	$222.70	$222.70
Purchase #7	$167.52	12.609%	$188.6426	$188.64	$188.65	$188.60
7 purchase totals =	$1,192.37		$1,275.2771	$1,275.28	$1,275.25	$1,275.10