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	$135.93	9.208%	$148.4464	$148.45	$148.45	$148.40
Purchase #2	$57.31	12.577%	$64.5179	$64.52	$64.50	$64.50
Purchase #3	$208.30	10.240%	$229.6299	$229.63	$229.65	$229.60
Purchase #4	$104.75	11.141%	$116.4202	$116.42	$116.40	$116.40
Purchase #5	$86.50	9.391%	$94.6232	$94.62	$94.60	$94.60
Purchase #6	$140.25	11.423%	$156.2708	$156.27	$156.25	$156.30
Purchase #7	$75.33	6.612%	$80.3108	$80.31	$80.30	$80.30
7 purchase totals =	$808.37		$890.2192	$890.22	$890.15	$890.10