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	$202.82	12.229%	$227.6229	$227.62	$227.60	$227.60
Purchase #2	$165.32	3.642%	$171.341	$171.34	$171.35	$171.30
Purchase #3	$226.40	6.247%	$240.5432	$240.54	$240.55	$240.50
Purchase #4	$241.34	12.589%	$271.7223	$271.72	$271.70	$271.70
Purchase #5	$240.57	9.852%	$264.271	$264.27	$264.25	$264.30
Purchase #6	$92.89	13.474%	$105.406	$105.41	$105.40	$105.40
Purchase #7	$151.51	10.286%	$167.0943	$167.09	$167.10	$167.10
7 purchase totals =	$1,320.85		$1,448.0007	$1,447.99	$1,447.95	$1,447.90