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	$35.26	6.406%	$37.5188	$37.52	$37.50	$37.50
Purchase #2	$164.84	4.337%	$171.9891	$171.99	$172.00	$172.00
Purchase #3	$229.80	11.158%	$255.4411	$255.44	$255.45	$255.40
Purchase #4	$180.80	12.721%	$203.7996	$203.80	$203.80	$203.80
Purchase #5	$41.72	6.576%	$44.4635	$44.46	$44.45	$44.50
Purchase #6	$96.57	13.594%	$109.6977	$109.70	$109.70	$109.70
Purchase #7	$152.54	13.410%	$172.9956	$173.00	$173.00	$173.00
7 purchase totals =	$901.53		$995.9054	$995.91	$995.90	$995.90