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	$43.83	4.676%	$45.8795	$45.88	$45.90	$45.90
Purchase #2	$150.61	7.809%	$162.3711	$162.37	$162.35	$162.40
Purchase #3	$74.29	12.250%	$83.3905	$83.39	$83.40	$83.40
Purchase #4	$158.54	13.793%	$180.4074	$180.41	$180.40	$180.40
Purchase #5	$25.55	13.667%	$29.0419	$29.04	$29.05	$29.00
Purchase #6	$209.69	10.296%	$231.2797	$231.28	$231.30	$231.30
Purchase #7	$61.92	9.828%	$68.0055	$68.01	$68.00	$68.00
7 purchase totals =	$724.43		$800.3756	$800.38	$800.40	$800.40