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	$82.30	8.131%	$88.9918	$88.99	$89.00	$89.00
Purchase #2	$32.57	5.546%	$34.3763	$34.38	$34.40	$34.40
Purchase #3	$85.93	13.656%	$97.6646	$97.66	$97.65	$97.70
Purchase #4	$14.27	7.707%	$15.3698	$15.37	$15.35	$15.40
Purchase #5	$243.86	7.241%	$261.5179	$261.52	$261.50	$261.50
Purchase #6	$199.51	11.459%	$222.3719	$222.37	$222.35	$222.40
Purchase #7	$162.96	10.569%	$180.1832	$180.18	$180.20	$180.20
7 purchase totals =	$821.40		$900.4755	$900.47	$900.45	$900.60