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	$115.89	4.485%	$121.0877	$121.09	$121.10	$121.10
Purchase #2	$38.27	10.581%	$42.3193	$42.32	$42.30	$42.30
Purchase #3	$115.27	10.663%	$127.5612	$127.56	$127.55	$127.60
Purchase #4	$56.84	8.369%	$61.5969	$61.60	$61.60	$61.60
Purchase #5	$20.75	11.143%	$23.0622	$23.06	$23.05	$23.10
Purchase #6	$155.83	4.537%	$162.9	$162.90	$162.90	$162.90
Purchase #7	$109.43	3.611%	$113.3815	$113.38	$113.40	$113.40
7 purchase totals =	$612.28		$651.9088	$651.91	$651.90	$652.00