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	$85.40	5.189%	$89.8314	$89.83	$89.85	$89.80
Purchase #2	$149.36	10.242%	$164.6575	$164.66	$164.65	$164.70
Purchase #3	$54.37	7.865%	$58.6462	$58.65	$58.65	$58.60
Purchase #4	$54.56	13.307%	$61.8203	$61.82	$61.80	$61.80
Purchase #5	$107.31	6.133%	$113.8913	$113.89	$113.90	$113.90
Purchase #6	$197.37	3.168%	$203.6227	$203.62	$203.60	$203.60
Purchase #7	$16.94	5.215%	$17.8234	$17.82	$17.80	$17.80
7 purchase totals =	$665.31		$710.2928	$710.29	$710.25	$710.20