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	$203.87	10.653%	$225.5883	$225.59	$225.60	$225.60
Purchase #2	$7.47	11.809%	$8.3521	$8.35	$8.35	$8.40
Purchase #3	$45.76	10.618%	$50.6188	$50.62	$50.60	$50.60
Purchase #4	$194.93	9.213%	$212.8889	$212.89	$212.90	$212.90
Purchase #5	$64.38	8.724%	$69.9965	$70.00	$70.00	$70.00
Purchase #6	$169.54	5.213%	$178.3781	$178.38	$178.40	$178.40
Purchase #7	$127.36	13.109%	$144.0556	$144.06	$144.05	$144.10
7 purchase totals =	$813.31		$889.8783	$889.89	$889.90	$890.00