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	$6.33	12.508%	$7.1218	$7.12	$7.10	$7.10
Purchase #2	$144.85	7.789%	$156.1324	$156.13	$156.15	$156.10
Purchase #3	$244.52	6.617%	$260.6999	$260.70	$260.70	$260.70
Purchase #4	$140.48	4.748%	$147.15	$147.15	$147.15	$147.20
Purchase #5	$128.35	7.239%	$137.6413	$137.64	$137.65	$137.60
Purchase #6	$219.53	10.491%	$242.5609	$242.56	$242.55	$242.60
Purchase #7	$77.81	5.588%	$82.158	$82.16	$82.15	$82.20
7 purchase totals =	$961.87		$1,033.4643	$1,033.46	$1,033.45	$1,033.50