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	$147.73	11.651%	$164.942	$164.94	$164.95	$164.90
Purchase #2	$142.37	13.495%	$161.5828	$161.58	$161.60	$161.60
Purchase #3	$167.52	10.703%	$185.4497	$185.45	$185.45	$185.40
Purchase #4	$50.41	4.474%	$52.6653	$52.67	$52.65	$52.70
Purchase #5	$89.81	5.429%	$94.6858	$94.69	$94.70	$94.70
Purchase #6	$74.38	11.549%	$82.9701	$82.97	$82.95	$83.00
Purchase #7	$52.35	10.432%	$57.8112	$57.81	$57.80	$57.80
7 purchase totals =	$724.57		$800.1069	$800.11	$800.10	$800.10