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	$144.33	12.185%	$161.9166	$161.92	$161.90	$161.90
Purchase #2	$108.74	13.806%	$123.7526	$123.75	$123.75	$123.80
Purchase #3	$225.79	3.364%	$233.3856	$233.39	$233.40	$233.40
Purchase #4	$17.25	7.719%	$18.5815	$18.58	$18.60	$18.60
Purchase #5	$175.46	3.764%	$182.0643	$182.06	$182.05	$182.10
Purchase #6	$82.95	8.520%	$90.0173	$90.02	$90.00	$90.00
Purchase #7	$73.63	12.693%	$82.9759	$82.98	$83.00	$83.00
7 purchase totals =	$828.15		$892.6938	$892.70	$892.70	$892.80