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	$173.39	8.651%	$188.39	$188.39	$188.40	$188.40
Purchase #2	$30.59	4.602%	$31.9978	$32.00	$32.00	$32.00
Purchase #3	$162.51	3.179%	$167.6762	$167.68	$167.70	$167.70
Purchase #4	$76.96	6.853%	$82.2341	$82.23	$82.25	$82.20
Purchase #5	$16.92	11.274%	$18.8276	$18.83	$18.85	$18.80
Purchase #6	$212.85	5.685%	$224.9505	$224.95	$224.95	$225.00
Purchase #7	$74.81	4.856%	$78.4428	$78.44	$78.45	$78.40
7 purchase totals =	$748.03		$792.5190	$792.52	$792.60	$792.50