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	$72.34	12.129%	$81.1141	$81.11	$81.10	$81.10
Purchase #2	$41.89	8.366%	$45.3945	$45.39	$45.40	$45.40
Purchase #3	$32.82	13.342%	$37.1988	$37.20	$37.20	$37.20
Purchase #4	$200.25	4.828%	$209.9181	$209.92	$209.90	$209.90
Purchase #5	$147.68	3.836%	$153.345	$153.35	$153.35	$153.30
Purchase #6	$136.92	13.716%	$155.6999	$155.70	$155.70	$155.70
Purchase #7	$52.66	13.320%	$59.6743	$59.67	$59.65	$59.70
7 purchase totals =	$684.56		$742.3447	$742.34	$742.30	$742.30