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	$89.89	10.293%	$99.1424	$99.14	$99.15	$99.10
Purchase #2	$17.90	10.550%	$19.7885	$19.79	$19.80	$19.80
Purchase #3	$38.47	13.541%	$43.6792	$43.68	$43.70	$43.70
Purchase #4	$188.36	13.588%	$213.9544	$213.95	$213.95	$214.00
Purchase #5	$117.41	11.677%	$131.12	$131.12	$131.10	$131.10
Purchase #6	$95.67	10.315%	$105.5384	$105.54	$105.55	$105.50
Purchase #7	$68.43	10.605%	$75.687	$75.69	$75.70	$75.70
7 purchase totals =	$616.13		$688.9099	$688.91	$688.95	$688.90