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	$78.76	5.240%	$82.887	$82.89	$82.90	$82.90
Purchase #2	$25.37	8.761%	$27.5927	$27.59	$27.60	$27.60
Purchase #3	$122.89	11.872%	$137.4795	$137.48	$137.50	$137.50
Purchase #4	$6.58	3.141%	$6.7867	$6.79	$6.80	$6.80
Purchase #5	$49.38	8.495%	$53.5748	$53.57	$53.55	$53.60
Purchase #6	$152.71	4.575%	$159.6965	$159.70	$159.70	$159.70
Purchase #7	$47.45	8.431%	$51.4505	$51.45	$51.45	$51.50
7 purchase totals =	$483.14		$519.4677	$519.47	$519.50	$519.60