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	$81.97	9.215%	$89.5235	$89.52	$89.50	$89.50
Purchase #2	$88.40	4.541%	$92.4142	$92.41	$92.40	$92.40
Purchase #3	$91.34	6.752%	$97.5073	$97.51	$97.50	$97.50
Purchase #4	$85.37	5.517%	$90.0799	$90.08	$90.10	$90.10
Purchase #5	$248.96	13.397%	$282.3132	$282.31	$282.30	$282.30
Purchase #6	$111.49	10.858%	$123.5956	$123.60	$123.60	$123.60
Purchase #7	$81.56	12.712%	$91.9279	$91.93	$91.95	$91.90
7 purchase totals =	$789.09		$867.3616	$867.36	$867.35	$867.30