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	$63.78	7.243%	$68.3996	$68.40	$68.40	$68.40
Purchase #2	$239.53	6.647%	$255.4516	$255.45	$255.45	$255.50
Purchase #3	$242.53	13.199%	$274.5415	$274.54	$274.55	$274.50
Purchase #4	$35.99	3.592%	$37.2828	$37.28	$37.30	$37.30
Purchase #5	$157.45	6.105%	$167.0623	$167.06	$167.05	$167.10
Purchase #6	$169.50	12.297%	$190.3434	$190.34	$190.35	$190.30
Purchase #7	$180.75	8.335%	$195.8155	$195.82	$195.80	$195.80
7 purchase totals =	$1,089.53		$1,188.8967	$1,188.89	$1,188.90	$1,188.90