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	$219.49	6.548%	$233.8622	$233.86	$233.85	$233.90
Purchase #2	$117.68	12.169%	$132.0005	$132.00	$132.00	$132.00
Purchase #3	$159.29	5.778%	$168.4938	$168.49	$168.50	$168.50
Purchase #4	$40.40	11.872%	$45.1963	$45.20	$45.20	$45.20
Purchase #5	$174.47	7.500%	$187.5553	$187.56	$187.55	$187.60
Purchase #6	$168.75	6.870%	$180.3431	$180.34	$180.35	$180.30
Purchase #7	$41.71	8.874%	$45.4113	$45.41	$45.40	$45.40
7 purchase totals =	$921.79		$992.8625	$992.86	$992.85	$992.90