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	$225.43	13.516%	$255.8991	$255.90	$255.90	$255.90
Purchase #2	$32.44	11.157%	$36.0593	$36.06	$36.05	$36.10
Purchase #3	$112.61	13.434%	$127.738	$127.74	$127.75	$127.70
Purchase #4	$30.91	12.680%	$34.8294	$34.83	$34.85	$34.80
Purchase #5	$96.37	4.109%	$100.3298	$100.33	$100.35	$100.30
Purchase #6	$81.55	5.417%	$85.9676	$85.97	$85.95	$86.00
Purchase #7	$199.73	13.491%	$226.6756	$226.68	$226.70	$226.70
7 purchase totals =	$779.04		$867.4988	$867.51	$867.55	$867.50