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	$29.35	13.510%	$33.3152	$33.32	$33.30	$33.30
Purchase #2	$81.92	8.725%	$89.0675	$89.07	$89.05	$89.10
Purchase #3	$224.61	13.465%	$254.8537	$254.85	$254.85	$254.90
Purchase #4	$76.40	9.793%	$83.8819	$83.88	$83.90	$83.90
Purchase #5	$7.44	5.164%	$7.8242	$7.82	$7.80	$7.80
Purchase #6	$62.46	6.612%	$66.5899	$66.59	$66.60	$66.60
Purchase #7	$148.77	11.614%	$166.0481	$166.05	$166.05	$166.00
7 purchase totals =	$630.95		$701.5805	$701.58	$701.55	$701.60