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	$122.87	13.869%	$139.9108	$139.91	$139.90	$139.90
Purchase #2	$64.96	13.180%	$73.5217	$73.52	$73.50	$73.50
Purchase #3	$64.53	11.317%	$71.8329	$71.83	$71.85	$71.80
Purchase #4	$151.41	11.357%	$168.6056	$168.61	$168.60	$168.60
Purchase #5	$235.88	12.634%	$265.6811	$265.68	$265.70	$265.70
Purchase #6	$53.96	10.343%	$59.5411	$59.54	$59.55	$59.50
Purchase #7	$27.91	7.370%	$29.967	$29.97	$29.95	$30.00
7 purchase totals =	$721.52		$809.0602	$809.06	$809.05	$809.00