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	$30.49	10.120%	$33.5756	$33.58	$33.60	$33.60
Purchase #2	$187.69	6.431%	$199.7603	$199.76	$199.75	$199.80
Purchase #3	$150.90	11.215%	$167.8234	$167.82	$167.80	$167.80
Purchase #4	$143.66	3.684%	$148.9524	$148.95	$148.95	$149.00
Purchase #5	$216.53	11.553%	$241.5457	$241.55	$241.55	$241.50
Purchase #6	$110.38	4.193%	$115.0082	$115.01	$115.00	$115.00
Purchase #7	$102.30	9.204%	$111.7157	$111.72	$111.70	$111.70
7 purchase totals =	$941.95		$1,018.3813	$1,018.39	$1,018.35	$1,018.40