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	$23.51	5.736%	$24.8585	$24.86	$24.85	$24.90
Purchase #2	$41.92	4.665%	$43.8756	$43.88	$43.90	$43.90
Purchase #3	$88.82	8.746%	$96.5882	$96.59	$96.60	$96.60
Purchase #4	$217.42	11.717%	$242.8951	$242.90	$242.90	$242.90
Purchase #5	$99.67	8.242%	$107.8848	$107.88	$107.90	$107.90
Purchase #6	$42.92	10.761%	$47.5386	$47.54	$47.55	$47.50
Purchase #7	$237.66	7.363%	$255.1589	$255.16	$255.15	$255.20
7 purchase totals =	$751.92		$818.7997	$818.81	$818.85	$818.90