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	$155.36	13.466%	$176.2808	$176.28	$176.30	$176.30
Purchase #2	$91.43	9.281%	$99.9156	$99.92	$99.90	$99.90
Purchase #3	$135.39	7.700%	$145.815	$145.82	$145.80	$145.80
Purchase #4	$218.88	12.419%	$246.0627	$246.06	$246.05	$246.10
Purchase #5	$233.60	6.688%	$249.2232	$249.22	$249.20	$249.20
Purchase #6	$155.66	4.325%	$162.3923	$162.39	$162.40	$162.40
Purchase #7	$103.25	13.453%	$117.1402	$117.14	$117.15	$117.10
7 purchase totals =	$1,093.57		$1,196.8298	$1,196.83	$1,196.80	$1,196.80