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	$149.41	12.371%	$167.8935	$167.89	$167.90	$167.90
Purchase #2	$132.44	11.764%	$148.0202	$148.02	$148.00	$148.00
Purchase #3	$173.40	7.579%	$186.542	$186.54	$186.55	$186.50
Purchase #4	$24.47	4.650%	$25.6079	$25.61	$25.60	$25.60
Purchase #5	$33.72	6.103%	$35.7779	$35.78	$35.80	$35.80
Purchase #6	$234.47	10.330%	$258.6908	$258.69	$258.70	$258.70
Purchase #7	$247.62	7.800%	$266.9344	$266.93	$266.95	$266.90
7 purchase totals =	$995.53		$1,089.4667	$1,089.46	$1,089.50	$1,089.40