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	$90.30	10.555%	$99.8312	$99.83	$99.85	$99.80
Purchase #2	$106.89	8.322%	$115.7854	$115.79	$115.80	$115.80
Purchase #3	$66.46	3.641%	$68.8798	$68.88	$68.90	$68.90
Purchase #4	$158.30	5.240%	$166.5949	$166.59	$166.60	$166.60
Purchase #5	$49.50	8.854%	$53.8827	$53.88	$53.90	$53.90
Purchase #6	$235.84	11.728%	$263.4993	$263.50	$263.50	$263.50
Purchase #7	$203.89	12.224%	$228.8135	$228.81	$228.80	$228.80
7 purchase totals =	$911.18		$997.2868	$997.28	$997.35	$997.30