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	$32.43	3.175%	$33.4597	$33.46	$33.45	$33.50
Purchase #2	$199.54	3.245%	$206.0151	$206.02	$206.00	$206.00
Purchase #3	$131.64	4.329%	$137.3387	$137.34	$137.35	$137.30
Purchase #4	$14.46	10.116%	$15.9228	$15.92	$15.90	$15.90
Purchase #5	$172.35	13.227%	$195.1467	$195.15	$195.15	$195.10
Purchase #6	$58.55	6.380%	$62.2855	$62.29	$62.30	$62.30
Purchase #7	$28.55	4.449%	$29.8202	$29.82	$29.80	$29.80
7 purchase totals =	$637.52		$679.9887	$680.00	$679.95	$679.90