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	$72.58	13.183%	$82.1482	$82.15	$82.15	$82.10
Purchase #2	$74.60	5.800%	$78.9268	$78.93	$78.95	$78.90
Purchase #3	$115.66	11.830%	$129.3426	$129.34	$129.35	$129.30
Purchase #4	$242.27	12.506%	$272.5683	$272.57	$272.55	$272.60
Purchase #5	$25.35	11.535%	$28.2741	$28.27	$28.25	$28.30
Purchase #6	$135.82	6.553%	$144.7203	$144.72	$144.70	$144.70
Purchase #7	$70.45	10.353%	$77.7437	$77.74	$77.75	$77.70
7 purchase totals =	$736.73		$813.7240	$813.72	$813.70	$813.60