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	$85.32	5.456%	$89.9751	$89.98	$90.00	$90.00
Purchase #2	$218.32	10.826%	$241.9553	$241.96	$241.95	$242.00
Purchase #3	$75.99	7.156%	$81.4278	$81.43	$81.45	$81.40
Purchase #4	$103.64	7.674%	$111.5933	$111.59	$111.60	$111.60
Purchase #5	$92.59	4.199%	$96.4779	$96.48	$96.50	$96.50
Purchase #6	$204.92	3.604%	$212.3053	$212.31	$212.30	$212.30
Purchase #7	$102.73	13.668%	$116.7711	$116.77	$116.75	$116.80
7 purchase totals =	$883.51		$950.5058	$950.52	$950.55	$950.60