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	$103.25	12.326%	$115.9766	$115.98	$116.00	$116.00
Purchase #2	$237.42	13.807%	$270.2006	$270.20	$270.20	$270.20
Purchase #3	$6.36	7.167%	$6.8158	$6.82	$6.80	$6.80
Purchase #4	$200.28	4.304%	$208.9001	$208.90	$208.90	$208.90
Purchase #5	$89.81	12.397%	$100.9437	$100.94	$100.95	$100.90
Purchase #6	$77.84	9.615%	$85.3243	$85.32	$85.30	$85.30
Purchase #7	$33.41	13.108%	$37.7894	$37.79	$37.80	$37.80
7 purchase totals =	$748.37		$825.9505	$825.95	$825.95	$825.90