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	$43.82	11.300%	$48.7717	$48.77	$48.75	$48.80
Purchase #2	$18.78	11.562%	$20.9513	$20.95	$20.95	$21.00
Purchase #3	$141.45	13.492%	$160.5344	$160.53	$160.55	$160.50
Purchase #4	$45.66	13.707%	$51.9186	$51.92	$51.90	$51.90
Purchase #5	$137.99	4.874%	$144.7156	$144.72	$144.70	$144.70
Purchase #6	$13.34	3.119%	$13.7561	$13.76	$13.75	$13.80
Purchase #7	$75.32	8.290%	$81.564	$81.56	$81.55	$81.60
7 purchase totals =	$476.36		$522.2117	$522.21	$522.15	$522.30