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	$170.89	10.398%	$188.6591	$188.66	$188.65	$188.70
Purchase #2	$220.32	13.732%	$250.5743	$250.57	$250.55	$250.60
Purchase #3	$178.43	12.364%	$200.4911	$200.49	$200.50	$200.50
Purchase #4	$118.25	12.253%	$132.7392	$132.74	$132.75	$132.70
Purchase #5	$17.84	13.414%	$20.2331	$20.23	$20.25	$20.20
Purchase #6	$199.96	11.421%	$222.7974	$222.80	$222.80	$222.80
Purchase #7	$193.79	9.142%	$211.5063	$211.51	$211.50	$211.50
7 purchase totals =	$1,099.48		$1,227.0005	$1,227.00	$1,227.00	$1,227.00