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	$235.34	8.520%	$255.391	$255.39	$255.40	$255.40
Purchase #2	$82.42	10.331%	$90.9348	$90.93	$90.95	$90.90
Purchase #3	$57.36	10.309%	$63.2732	$63.27	$63.25	$63.30
Purchase #4	$202.47	7.854%	$218.372	$218.37	$218.35	$218.40
Purchase #5	$118.89	4.472%	$124.2068	$124.21	$124.20	$124.20
Purchase #6	$57.92	6.818%	$61.869	$61.87	$61.85	$61.90
Purchase #7	$148.96	13.110%	$168.4887	$168.49	$168.50	$168.50
7 purchase totals =	$903.36		$982.5355	$982.53	$982.50	$982.60