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	$56.31	5.848%	$59.603	$59.60	$59.60	$59.60
Purchase #2	$222.71	4.801%	$233.4023	$233.40	$233.40	$233.40
Purchase #3	$108.49	7.860%	$117.0173	$117.02	$117.00	$117.00
Purchase #4	$136.67	10.310%	$150.7607	$150.76	$150.75	$150.80
Purchase #5	$9.59	5.268%	$10.0952	$10.10	$10.10	$10.10
Purchase #6	$35.88	4.109%	$37.3543	$37.35	$37.35	$37.40
Purchase #7	$110.83	9.697%	$121.5772	$121.58	$121.60	$121.60
7 purchase totals =	$680.48		$729.8100	$729.81	$729.80	$729.90