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	$91.67	9.340%	$100.232	$100.23	$100.25	$100.20
Purchase #2	$104.75	13.484%	$118.8745	$118.87	$118.85	$118.90
Purchase #3	$137.76	9.128%	$150.3347	$150.33	$150.35	$150.30
Purchase #4	$168.66	6.250%	$179.2013	$179.20	$179.20	$179.20
Purchase #5	$18.79	7.827%	$20.2607	$20.26	$20.25	$20.30
Purchase #6	$221.79	7.703%	$238.8745	$238.87	$238.85	$238.90
Purchase #7	$179.31	10.756%	$198.5966	$198.60	$198.60	$198.60
7 purchase totals =	$922.73		$1,006.3743	$1,006.36	$1,006.35	$1,006.40