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	$127.97	13.784%	$145.6094	$145.61	$145.60	$145.60
Purchase #2	$60.87	6.601%	$64.888	$64.89	$64.90	$64.90
Purchase #3	$159.87	4.478%	$167.029	$167.03	$167.05	$167.00
Purchase #4	$98.27	13.755%	$111.787	$111.79	$111.80	$111.80
Purchase #5	$23.52	4.159%	$24.4982	$24.50	$24.50	$24.50
Purchase #6	$124.40	13.351%	$141.0086	$141.01	$141.00	$141.00
Purchase #7	$171.42	7.264%	$183.8719	$183.87	$183.85	$183.90
7 purchase totals =	$766.32		$838.6921	$838.70	$838.70	$838.70