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	$57.31	9.193%	$62.5785	$62.58	$62.60	$62.60
Purchase #2	$50.88	7.340%	$54.6146	$54.61	$54.60	$54.60
Purchase #3	$78.58	9.140%	$85.7622	$85.76	$85.75	$85.80
Purchase #4	$220.72	3.437%	$228.3061	$228.31	$228.30	$228.30
Purchase #5	$28.25	10.493%	$31.2143	$31.21	$31.20	$31.20
Purchase #6	$125.45	9.518%	$137.3903	$137.39	$137.40	$137.40
Purchase #7	$42.80	3.495%	$44.2959	$44.30	$44.30	$44.30
7 purchase totals =	$603.99		$644.1619	$644.16	$644.15	$644.20