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	$24.63	11.503%	$27.4632	$27.46	$27.45	$27.50
Purchase #2	$250.90	7.131%	$268.7917	$268.79	$268.80	$268.80
Purchase #3	$66.27	6.395%	$70.508	$70.51	$70.50	$70.50
Purchase #4	$77.60	11.657%	$86.6458	$86.65	$86.65	$86.60
Purchase #5	$227.59	7.143%	$243.8468	$243.85	$243.85	$243.80
Purchase #6	$133.59	9.493%	$146.2717	$146.27	$146.25	$146.30
Purchase #7	$76.66	4.671%	$80.2408	$80.24	$80.25	$80.20
7 purchase totals =	$857.24		$923.7680	$923.77	$923.75	$923.70