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	$41.50	9.871%	$45.5965	$45.60	$45.60	$45.60
Purchase #2	$36.54	3.277%	$37.7374	$37.74	$37.75	$37.70
Purchase #3	$25.72	13.507%	$29.194	$29.19	$29.20	$29.20
Purchase #4	$101.37	12.589%	$114.1315	$114.13	$114.15	$114.10
Purchase #5	$152.51	8.286%	$165.147	$165.15	$165.15	$165.10
Purchase #6	$83.73	8.677%	$90.9953	$91.00	$91.00	$91.00
Purchase #7	$101.70	3.331%	$105.0876	$105.09	$105.10	$105.10
7 purchase totals =	$543.07		$587.8893	$587.90	$587.95	$587.80