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	$85.93	4.337%	$89.6568	$89.66	$89.65	$89.70
Purchase #2	$78.78	6.650%	$84.0189	$84.02	$84.00	$84.00
Purchase #3	$172.61	4.117%	$179.7164	$179.72	$179.70	$179.70
Purchase #4	$66.94	7.616%	$72.0382	$72.04	$72.05	$72.00
Purchase #5	$166.69	11.670%	$186.1427	$186.14	$186.15	$186.10
Purchase #6	$148.28	3.789%	$153.8983	$153.90	$153.90	$153.90
Purchase #7	$97.34	12.673%	$109.6759	$109.68	$109.70	$109.70
7 purchase totals =	$816.57		$875.1472	$875.16	$875.15	$875.10