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	$87.71	13.359%	$99.4272	$99.43	$99.45	$99.40
Purchase #2	$159.53	12.497%	$179.4665	$179.47	$179.45	$179.50
Purchase #3	$79.94	5.331%	$84.2016	$84.20	$84.20	$84.20
Purchase #4	$136.56	3.451%	$141.2727	$141.27	$141.25	$141.30
Purchase #5	$40.94	6.552%	$43.6224	$43.62	$43.60	$43.60
Purchase #6	$226.29	13.147%	$256.0403	$256.04	$256.05	$256.00
Purchase #7	$82.50	3.740%	$85.5855	$85.59	$85.60	$85.60
7 purchase totals =	$813.47		$889.6162	$889.62	$889.60	$889.60