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	$245.86	13.789%	$279.7616	$279.76	$279.75	$279.80
Purchase #2	$247.31	9.697%	$271.2917	$271.29	$271.30	$271.30
Purchase #3	$27.89	3.626%	$28.9013	$28.90	$28.90	$28.90
Purchase #4	$81.49	5.466%	$85.9442	$85.94	$85.95	$85.90
Purchase #5	$120.67	5.295%	$127.0595	$127.06	$127.05	$127.10
Purchase #6	$48.86	10.663%	$54.0699	$54.07	$54.05	$54.10
Purchase #7	$102.79	5.419%	$108.3602	$108.36	$108.35	$108.40
7 purchase totals =	$874.87		$955.3884	$955.38	$955.35	$955.50