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	$231.32	10.468%	$255.5346	$255.53	$255.55	$255.50
Purchase #2	$223.84	9.466%	$245.0287	$245.03	$245.05	$245.00
Purchase #3	$101.72	10.239%	$112.1351	$112.14	$112.15	$112.10
Purchase #4	$37.41	7.756%	$40.3115	$40.31	$40.30	$40.30
Purchase #5	$198.89	13.521%	$225.7819	$225.78	$225.80	$225.80
Purchase #6	$144.50	7.119%	$154.787	$154.79	$154.80	$154.80
Purchase #7	$157.36	13.431%	$178.495	$178.50	$178.50	$178.50
7 purchase totals =	$1,095.04		$1,212.0738	$1,212.08	$1,212.15	$1,212.00