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	$95.54	3.736%	$99.1094	$99.11	$99.10	$99.10
Purchase #2	$139.41	5.761%	$147.4414	$147.44	$147.45	$147.40
Purchase #3	$62.48	6.326%	$66.4325	$66.43	$66.45	$66.40
Purchase #4	$163.68	9.405%	$179.0741	$179.07	$179.05	$179.10
Purchase #5	$55.94	5.701%	$59.1291	$59.13	$59.15	$59.10
Purchase #6	$126.28	5.162%	$132.7986	$132.80	$132.80	$132.80
Purchase #7	$83.90	12.740%	$94.5889	$94.59	$94.60	$94.60
7 purchase totals =	$727.23		$778.5740	$778.57	$778.60	$778.50