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	$121.26	9.592%	$132.8913	$132.89	$132.90	$132.90
Purchase #2	$160.95	4.690%	$168.4986	$168.50	$168.50	$168.50
Purchase #3	$57.30	10.156%	$63.1194	$63.12	$63.10	$63.10
Purchase #4	$215.45	7.591%	$231.8048	$231.80	$231.80	$231.80
Purchase #5	$79.30	13.717%	$90.1776	$90.18	$90.20	$90.20
Purchase #6	$79.42	4.278%	$82.8176	$82.82	$82.80	$82.80
Purchase #7	$102.47	7.208%	$109.856	$109.86	$109.85	$109.90
7 purchase totals =	$816.15		$879.1653	$879.17	$879.15	$879.20