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	$12.27	13.258%	$13.8968	$13.90	$13.90	$13.90
Purchase #2	$231.38	8.300%	$250.5845	$250.58	$250.60	$250.60
Purchase #3	$58.59	4.412%	$61.175	$61.18	$61.20	$61.20
Purchase #4	$165.52	7.130%	$177.3216	$177.32	$177.30	$177.30
Purchase #5	$90.73	10.337%	$100.1088	$100.11	$100.10	$100.10
Purchase #6	$249.74	9.252%	$272.8459	$272.85	$272.85	$272.80
Purchase #7	$63.36	4.855%	$66.4361	$66.44	$66.45	$66.40
7 purchase totals =	$871.59		$942.3687	$942.38	$942.40	$942.30