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	$124.86	6.195%	$132.5951	$132.60	$132.60	$132.60
Purchase #2	$168.37	12.300%	$189.0795	$189.08	$189.10	$189.10
Purchase #3	$96.56	3.750%	$100.181	$100.18	$100.20	$100.20
Purchase #4	$225.48	13.221%	$255.2907	$255.29	$255.30	$255.30
Purchase #5	$237.27	5.188%	$249.5796	$249.58	$249.60	$249.60
Purchase #6	$25.98	4.405%	$27.1244	$27.12	$27.10	$27.10
Purchase #7	$128.47	13.868%	$146.2862	$146.29	$146.30	$146.30
7 purchase totals =	$1,006.99		$1,100.1365	$1,100.14	$1,100.20	$1,100.20