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	$99.32	3.604%	$102.8995	$102.90	$102.90	$102.90
Purchase #2	$228.90	12.854%	$258.3228	$258.32	$258.30	$258.30
Purchase #3	$154.34	5.472%	$162.7855	$162.79	$162.80	$162.80
Purchase #4	$192.67	11.493%	$214.8136	$214.81	$214.80	$214.80
Purchase #5	$200.28	12.542%	$225.3991	$225.40	$225.40	$225.40
Purchase #6	$196.73	13.288%	$222.8715	$222.87	$222.85	$222.90
Purchase #7	$173.82	3.608%	$180.0914	$180.09	$180.10	$180.10
7 purchase totals =	$1,246.06		$1,367.1834	$1,367.18	$1,367.15	$1,367.20