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	$139.44	4.648%	$145.9212	$145.92	$145.90	$145.90
Purchase #2	$135.47	12.828%	$152.8481	$152.85	$152.85	$152.80
Purchase #3	$147.74	9.602%	$161.926	$161.93	$161.95	$161.90
Purchase #4	$99.48	12.514%	$111.9289	$111.93	$111.95	$111.90
Purchase #5	$62.43	5.746%	$66.0172	$66.02	$66.00	$66.00
Purchase #6	$25.43	11.218%	$28.2827	$28.28	$28.30	$28.30
Purchase #7	$31.47	7.665%	$33.8822	$33.88	$33.90	$33.90
7 purchase totals =	$641.46		$700.8063	$700.81	$700.85	$700.70