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	$111.70	6.166%	$118.5874	$118.59	$118.60	$118.60
Purchase #2	$46.60	9.118%	$50.849	$50.85	$50.85	$50.80
Purchase #3	$130.43	4.635%	$136.4754	$136.48	$136.50	$136.50
Purchase #4	$41.97	11.647%	$46.8582	$46.86	$46.85	$46.90
Purchase #5	$95.30	12.793%	$107.4917	$107.49	$107.50	$107.50
Purchase #6	$174.89	6.506%	$186.2683	$186.27	$186.25	$186.30
Purchase #7	$6.82	5.257%	$7.1785	$7.18	$7.20	$7.20
7 purchase totals =	$607.71		$653.7085	$653.72	$653.75	$653.80