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	$81.84	6.297%	$86.9935	$86.99	$87.00	$87.00
Purchase #2	$112.82	5.345%	$118.8502	$118.85	$118.85	$118.90
Purchase #3	$105.32	5.728%	$111.3527	$111.35	$111.35	$111.40
Purchase #4	$89.92	10.258%	$99.144	$99.14	$99.15	$99.10
Purchase #5	$76.74	13.174%	$86.8497	$86.85	$86.85	$86.80
Purchase #6	$173.67	8.464%	$188.3694	$188.37	$188.35	$188.40
Purchase #7	$169.69	13.321%	$192.2944	$192.29	$192.30	$192.30
7 purchase totals =	$810.00		$883.8539	$883.84	$883.85	$883.90