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	$166.38	8.677%	$180.8168	$180.82	$180.80	$180.80
Purchase #2	$93.84	13.613%	$106.6144	$106.61	$106.60	$106.60
Purchase #3	$185.99	12.541%	$209.315	$209.32	$209.30	$209.30
Purchase #4	$162.43	7.812%	$175.119	$175.12	$175.10	$175.10
Purchase #5	$205.66	8.862%	$223.8856	$223.89	$223.90	$223.90
Purchase #6	$45.43	10.381%	$50.1461	$50.15	$50.15	$50.10
Purchase #7	$67.35	8.366%	$72.9845	$72.98	$73.00	$73.00
7 purchase totals =	$927.08		$1,018.8814	$1,018.89	$1,018.85	$1,018.80