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	$51.31	4.423%	$53.5794	$53.58	$53.60	$53.60
Purchase #2	$142.80	5.315%	$150.3898	$150.39	$150.40	$150.40
Purchase #3	$115.62	4.432%	$120.7443	$120.74	$120.75	$120.70
Purchase #4	$23.36	13.599%	$26.5367	$26.54	$26.55	$26.50
Purchase #5	$68.66	5.124%	$72.1781	$72.18	$72.20	$72.20
Purchase #6	$115.78	10.421%	$127.8454	$127.85	$127.85	$127.80
Purchase #7	$109.76	3.697%	$113.8178	$113.82	$113.80	$113.80
7 purchase totals =	$627.29		$665.0915	$665.10	$665.15	$665.00