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	$124.49	10.743%	$137.864	$137.86	$137.85	$137.90
Purchase #2	$61.73	8.404%	$66.9178	$66.92	$66.90	$66.90
Purchase #3	$94.75	6.193%	$100.6179	$100.62	$100.60	$100.60
Purchase #4	$132.60	11.436%	$147.7641	$147.76	$147.75	$147.80
Purchase #5	$28.30	13.678%	$32.1709	$32.17	$32.15	$32.20
Purchase #6	$168.82	7.595%	$181.6419	$181.64	$181.65	$181.60
Purchase #7	$66.55	10.407%	$73.4759	$73.48	$73.50	$73.50
7 purchase totals =	$677.24		$740.4525	$740.45	$740.40	$740.50