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	$109.65	11.658%	$122.433	$122.43	$122.45	$122.40
Purchase #2	$52.90	4.863%	$55.4725	$55.47	$55.45	$55.50
Purchase #3	$132.42	12.165%	$148.5289	$148.53	$148.55	$148.50
Purchase #4	$118.30	3.330%	$122.2394	$122.24	$122.25	$122.20
Purchase #5	$146.83	3.615%	$152.1379	$152.14	$152.15	$152.10
Purchase #6	$165.70	5.693%	$175.1333	$175.13	$175.15	$175.10
Purchase #7	$42.50	3.300%	$43.9025	$43.90	$43.90	$43.90
7 purchase totals =	$768.30		$819.8475	$819.84	$819.90	$819.70