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	$27.71	6.560%	$29.5278	$29.53	$29.55	$29.50
Purchase #2	$227.64	6.728%	$242.9556	$242.96	$242.95	$243.00
Purchase #3	$35.49	7.699%	$38.2224	$38.22	$38.20	$38.20
Purchase #4	$218.47	3.174%	$225.4042	$225.40	$225.40	$225.40
Purchase #5	$35.80	4.248%	$37.3208	$37.32	$37.30	$37.30
Purchase #6	$67.67	13.507%	$76.8102	$76.81	$76.80	$76.80
Purchase #7	$81.90	10.374%	$90.3963	$90.40	$90.40	$90.40
7 purchase totals =	$694.68		$740.6373	$740.64	$740.60	$740.60