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	$78.48	9.188%	$85.6907	$85.69	$85.70	$85.70
Purchase #2	$133.69	11.857%	$149.5416	$149.54	$149.55	$149.50
Purchase #3	$171.35	10.246%	$188.9065	$188.91	$188.90	$188.90
Purchase #4	$103.58	3.768%	$107.4829	$107.48	$107.50	$107.50
Purchase #5	$137.85	10.789%	$152.7226	$152.72	$152.70	$152.70
Purchase #6	$64.38	11.686%	$71.9034	$71.90	$71.90	$71.90
Purchase #7	$48.60	12.152%	$54.5059	$54.51	$54.50	$54.50
7 purchase totals =	$737.93		$810.7536	$810.75	$810.75	$810.70