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	$49.79	10.174%	$54.8556	$54.86	$54.85	$54.90
Purchase #2	$88.66	10.799%	$98.2344	$98.23	$98.25	$98.20
Purchase #3	$143.91	6.402%	$153.1231	$153.12	$153.10	$153.10
Purchase #4	$137.94	9.122%	$150.5229	$150.52	$150.50	$150.50
Purchase #5	$179.32	5.421%	$189.0409	$189.04	$189.05	$189.00
Purchase #6	$128.67	10.285%	$141.9037	$141.90	$141.90	$141.90
Purchase #7	$117.68	4.104%	$122.5096	$122.51	$122.50	$122.50
7 purchase totals =	$845.97		$910.1902	$910.18	$910.15	$910.10