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	$67.76	6.741%	$72.3277	$72.33	$72.35	$72.30
Purchase #2	$120.37	5.775%	$127.3214	$127.32	$127.30	$127.30
Purchase #3	$40.31	11.135%	$44.7985	$44.80	$44.80	$44.80
Purchase #4	$73.86	10.848%	$81.8723	$81.87	$81.85	$81.90
Purchase #5	$15.90	13.794%	$18.0932	$18.09	$18.10	$18.10
Purchase #6	$107.77	11.766%	$120.4502	$120.45	$120.45	$120.50
Purchase #7	$168.30	7.332%	$180.6398	$180.64	$180.65	$180.60
7 purchase totals =	$594.27		$645.5031	$645.50	$645.50	$645.50