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	$158.83	4.134%	$165.396	$165.40	$165.40	$165.40
Purchase #2	$155.90	6.410%	$165.8932	$165.89	$165.90	$165.90
Purchase #3	$12.81	9.816%	$14.0674	$14.07	$14.05	$14.10
Purchase #4	$215.90	11.457%	$240.6357	$240.64	$240.65	$240.60
Purchase #5	$87.34	8.176%	$94.4809	$94.48	$94.50	$94.50
Purchase #6	$37.61	12.825%	$42.4335	$42.43	$42.45	$42.40
Purchase #7	$118.77	10.589%	$131.3466	$131.35	$131.35	$131.30
7 purchase totals =	$787.16		$854.2533	$854.26	$854.30	$854.20