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	$149.66	13.443%	$169.7788	$169.78	$169.80	$169.80
Purchase #2	$250.77	3.862%	$260.4547	$260.45	$260.45	$260.50
Purchase #3	$135.61	13.294%	$153.638	$153.64	$153.65	$153.60
Purchase #4	$165.55	3.569%	$171.4585	$171.46	$171.45	$171.50
Purchase #5	$32.50	10.261%	$35.8348	$35.83	$35.85	$35.80
Purchase #6	$50.79	3.870%	$52.7556	$52.76	$52.75	$52.80
Purchase #7	$49.90	13.518%	$56.6455	$56.65	$56.65	$56.60
7 purchase totals =	$834.78		$900.5659	$900.57	$900.60	$900.60