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	$104.77	8.250%	$113.4135	$113.41	$113.40	$113.40
Purchase #2	$112.59	3.490%	$116.5194	$116.52	$116.50	$116.50
Purchase #3	$135.80	7.532%	$146.0285	$146.03	$146.05	$146.00
Purchase #4	$90.36	3.631%	$93.641	$93.64	$93.65	$93.60
Purchase #5	$187.27	4.744%	$196.1541	$196.15	$196.15	$196.20
Purchase #6	$91.78	8.866%	$99.9172	$99.92	$99.90	$99.90
Purchase #7	$20.45	8.847%	$22.2592	$22.26	$22.25	$22.30
7 purchase totals =	$743.02		$787.9329	$787.93	$787.90	$787.90