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	$85.92	5.349%	$90.5159	$90.52	$90.50	$90.50
Purchase #2	$75.71	12.455%	$85.1397	$85.14	$85.15	$85.10
Purchase #3	$73.46	3.759%	$76.2214	$76.22	$76.20	$76.20
Purchase #4	$58.28	13.255%	$66.005	$66.01	$66.00	$66.00
Purchase #5	$66.59	10.581%	$73.6359	$73.64	$73.65	$73.60
Purchase #6	$99.92	12.400%	$112.3101	$112.31	$112.30	$112.30
Purchase #7	$125.74	7.280%	$134.8939	$134.89	$134.90	$134.90
7 purchase totals =	$585.62		$638.7219	$638.73	$638.70	$638.60