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	$39.30	8.147%	$42.5018	$42.50	$42.50	$42.50
Purchase #2	$146.87	3.833%	$152.4995	$152.50	$152.50	$152.50
Purchase #3	$198.89	9.713%	$218.2082	$218.21	$218.20	$218.20
Purchase #4	$132.36	10.510%	$146.271	$146.27	$146.25	$146.30
Purchase #5	$206.34	6.725%	$220.2164	$220.22	$220.20	$220.20
Purchase #6	$106.74	5.250%	$112.3439	$112.34	$112.35	$112.30
Purchase #7	$102.39	10.713%	$113.359	$113.36	$113.35	$113.40
7 purchase totals =	$932.89		$1,005.3998	$1,005.40	$1,005.35	$1,005.40