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	$195.34	12.425%	$219.611	$219.61	$219.60	$219.60
Purchase #2	$169.99	11.867%	$190.1627	$190.16	$190.15	$190.20
Purchase #3	$73.34	7.638%	$78.9417	$78.94	$78.95	$78.90
Purchase #4	$101.33	6.631%	$108.0492	$108.05	$108.05	$108.00
Purchase #5	$135.86	7.196%	$145.6365	$145.64	$145.65	$145.60
Purchase #6	$39.66	10.591%	$43.8604	$43.86	$43.85	$43.90
Purchase #7	$104.94	7.601%	$112.9165	$112.92	$112.90	$112.90
7 purchase totals =	$820.46		$899.1780	$899.18	$899.15	$899.10