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	$249.61	9.152%	$272.4543	$272.45	$272.45	$272.50
Purchase #2	$135.69	7.303%	$145.5994	$145.60	$145.60	$145.60
Purchase #3	$85.85	8.783%	$93.3902	$93.39	$93.40	$93.40
Purchase #4	$94.43	6.460%	$100.5302	$100.53	$100.55	$100.50
Purchase #5	$99.57	3.666%	$103.2202	$103.22	$103.20	$103.20
Purchase #6	$168.72	8.211%	$182.5736	$182.57	$182.55	$182.60
Purchase #7	$200.83	3.624%	$208.1081	$208.11	$208.10	$208.10
7 purchase totals =	$1,034.70		$1,105.8760	$1,105.87	$1,105.85	$1,105.90