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	$231.90	10.642%	$256.5788	$256.58	$256.60	$256.60
Purchase #2	$124.76	5.352%	$131.4372	$131.44	$131.45	$131.40
Purchase #3	$145.31	6.147%	$154.2422	$154.24	$154.25	$154.20
Purchase #4	$189.84	4.433%	$198.2556	$198.26	$198.25	$198.30
Purchase #5	$131.97	5.480%	$139.202	$139.20	$139.20	$139.20
Purchase #6	$88.92	13.116%	$100.5827	$100.58	$100.60	$100.60
Purchase #7	$41.53	3.354%	$42.9229	$42.92	$42.90	$42.90
7 purchase totals =	$954.23		$1,023.2214	$1,023.22	$1,023.25	$1,023.20