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	$16.55	5.619%	$17.4799	$17.48	$17.50	$17.50
Purchase #2	$131.91	5.119%	$138.6625	$138.66	$138.65	$138.70
Purchase #3	$86.59	3.805%	$89.8847	$89.88	$89.90	$89.90
Purchase #4	$78.43	12.615%	$88.3239	$88.32	$88.30	$88.30
Purchase #5	$116.46	3.464%	$120.4942	$120.49	$120.50	$120.50
Purchase #6	$219.39	12.726%	$247.3096	$247.31	$247.30	$247.30
Purchase #7	$152.49	5.741%	$161.2445	$161.24	$161.25	$161.20
7 purchase totals =	$801.82		$863.3993	$863.38	$863.40	$863.40