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	$29.76	12.509%	$33.4827	$33.48	$33.50	$33.50
Purchase #2	$214.71	11.557%	$239.524	$239.52	$239.50	$239.50
Purchase #3	$78.50	6.471%	$83.5797	$83.58	$83.60	$83.60
Purchase #4	$53.61	9.658%	$58.7877	$58.79	$58.80	$58.80
Purchase #5	$126.86	11.722%	$141.7305	$141.73	$141.75	$141.70
Purchase #6	$142.31	13.647%	$161.731	$161.73	$161.75	$161.70
Purchase #7	$19.34	11.228%	$21.5115	$21.51	$21.50	$21.50
7 purchase totals =	$665.09		$740.3471	$740.34	$740.40	$740.30