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	$104.95	11.124%	$116.6246	$116.62	$116.60	$116.60
Purchase #2	$136.75	11.524%	$152.5091	$152.51	$152.50	$152.50
Purchase #3	$82.89	9.209%	$90.5233	$90.52	$90.50	$90.50
Purchase #4	$184.28	10.764%	$204.1159	$204.12	$204.10	$204.10
Purchase #5	$36.97	12.389%	$41.5502	$41.55	$41.55	$41.60
Purchase #6	$8.59	13.600%	$9.7582	$9.76	$9.75	$9.80
Purchase #7	$218.64	4.694%	$228.903	$228.90	$228.90	$228.90
7 purchase totals =	$773.07		$843.9843	$843.98	$843.90	$844.00