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	$115.94	12.469%	$130.3966	$130.40	$130.40	$130.40
Purchase #2	$85.36	4.250%	$88.9878	$88.99	$89.00	$89.00
Purchase #3	$100.25	10.358%	$110.6339	$110.63	$110.65	$110.60
Purchase #4	$217.54	7.197%	$233.1964	$233.20	$233.20	$233.20
Purchase #5	$164.89	12.509%	$185.5161	$185.52	$185.50	$185.50
Purchase #6	$133.88	6.328%	$142.3519	$142.35	$142.35	$142.40
Purchase #7	$153.81	8.467%	$166.8331	$166.83	$166.85	$166.80
7 purchase totals =	$971.67		$1,057.9158	$1,057.92	$1,057.95	$1,057.90