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	$121.30	13.530%	$137.7119	$137.71	$137.70	$137.70
Purchase #2	$103.79	7.845%	$111.9323	$111.93	$111.95	$111.90
Purchase #3	$87.65	13.110%	$99.1409	$99.14	$99.15	$99.10
Purchase #4	$105.26	9.268%	$115.0155	$115.02	$115.00	$115.00
Purchase #5	$88.39	10.678%	$97.8283	$97.83	$97.85	$97.80
Purchase #6	$207.90	11.233%	$231.2534	$231.25	$231.25	$231.30
Purchase #7	$152.84	7.483%	$164.277	$164.28	$164.30	$164.30
7 purchase totals =	$867.13		$957.1593	$957.16	$957.20	$957.10