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	$30.71	10.166%	$33.832	$33.83	$33.85	$33.80
Purchase #2	$127.81	7.493%	$137.3868	$137.39	$137.40	$137.40
Purchase #3	$247.48	10.241%	$272.8244	$272.82	$272.80	$272.80
Purchase #4	$224.70	8.532%	$243.8714	$243.87	$243.85	$243.90
Purchase #5	$239.79	6.368%	$255.0598	$255.06	$255.05	$255.10
Purchase #6	$78.32	4.650%	$81.9619	$81.96	$81.95	$82.00
Purchase #7	$68.47	7.515%	$73.6155	$73.62	$73.60	$73.60
7 purchase totals =	$1,017.28		$1,098.5518	$1,098.55	$1,098.50	$1,098.60