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	$153.33	9.635%	$168.1033	$168.10	$168.10	$168.10
Purchase #2	$215.88	4.150%	$224.839	$224.84	$224.85	$224.80
Purchase #3	$141.69	10.662%	$156.797	$156.80	$156.80	$156.80
Purchase #4	$172.49	10.548%	$190.6842	$190.68	$190.70	$190.70
Purchase #5	$169.32	5.784%	$179.1135	$179.11	$179.10	$179.10
Purchase #6	$23.83	8.136%	$25.7688	$25.77	$25.75	$25.80
Purchase #7	$28.35	10.326%	$31.2774	$31.28	$31.30	$31.30
7 purchase totals =	$904.89		$976.5832	$976.58	$976.60	$976.60