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	$109.35	3.253%	$112.9072	$112.91	$112.90	$112.90
Purchase #2	$172.66	6.658%	$184.1557	$184.16	$184.15	$184.20
Purchase #3	$12.27	11.201%	$13.6444	$13.64	$13.65	$13.60
Purchase #4	$77.44	13.118%	$87.5986	$87.60	$87.60	$87.60
Purchase #5	$59.82	11.694%	$66.8154	$66.82	$66.80	$66.80
Purchase #6	$69.31	8.629%	$75.2908	$75.29	$75.30	$75.30
Purchase #7	$98.53	7.112%	$105.5375	$105.54	$105.55	$105.50
7 purchase totals =	$599.38		$645.9496	$645.96	$645.95	$645.90