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	$81.65	9.773%	$89.6297	$89.63	$89.65	$89.60
Purchase #2	$72.83	11.218%	$81.0001	$81.00	$81.00	$81.00
Purchase #3	$134.92	10.356%	$148.8923	$148.89	$148.90	$148.90
Purchase #4	$42.67	9.149%	$46.5739	$46.57	$46.55	$46.60
Purchase #5	$54.46	3.431%	$56.3285	$56.33	$56.35	$56.30
Purchase #6	$148.71	10.747%	$164.6919	$164.69	$164.70	$164.70
Purchase #7	$179.92	7.273%	$193.0056	$193.01	$193.00	$193.00
7 purchase totals =	$715.16		$780.1220	$780.12	$780.15	$780.10