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	$98.87	5.587%	$104.3939	$104.39	$104.40	$104.40
Purchase #2	$85.84	4.702%	$89.8762	$89.88	$89.90	$89.90
Purchase #3	$230.65	4.170%	$240.2681	$240.27	$240.25	$240.30
Purchase #4	$26.25	11.212%	$29.1932	$29.19	$29.20	$29.20
Purchase #5	$145.51	6.493%	$154.958	$154.96	$154.95	$155.00
Purchase #6	$130.41	8.413%	$141.3814	$141.38	$141.40	$141.40
Purchase #7	$77.46	10.844%	$85.8598	$85.86	$85.85	$85.90
7 purchase totals =	$794.99		$845.9306	$845.93	$845.95	$846.10