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	$116.54	6.128%	$123.6816	$123.68	$123.70	$123.70
Purchase #2	$64.31	3.112%	$66.3113	$66.31	$66.30	$66.30
Purchase #3	$197.54	13.145%	$223.5066	$223.51	$223.50	$223.50
Purchase #4	$10.63	12.686%	$11.9785	$11.98	$12.00	$12.00
Purchase #5	$94.86	10.593%	$104.9085	$104.91	$104.90	$104.90
Purchase #6	$234.48	3.150%	$241.8661	$241.87	$241.85	$241.90
Purchase #7	$36.92	6.599%	$39.3564	$39.36	$39.35	$39.40
7 purchase totals =	$755.28		$811.6090	$811.62	$811.60	$811.70