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	$108.34	3.505%	$112.1373	$112.14	$112.15	$112.10
Purchase #2	$100.55	12.760%	$113.3802	$113.38	$113.40	$113.40
Purchase #3	$102.55	13.737%	$116.6373	$116.64	$116.65	$116.60
Purchase #4	$20.68	4.845%	$21.6819	$21.68	$21.70	$21.70
Purchase #5	$87.96	5.549%	$92.8409	$92.84	$92.85	$92.80
Purchase #6	$73.41	7.368%	$78.8188	$78.82	$78.80	$78.80
Purchase #7	$226.82	3.837%	$235.5231	$235.52	$235.50	$235.50
7 purchase totals =	$720.31		$771.0195	$771.02	$771.05	$770.90