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	$63.54	5.294%	$66.9038	$66.90	$66.90	$66.90
Purchase #2	$245.37	12.226%	$275.3689	$275.37	$275.35	$275.40
Purchase #3	$112.85	13.250%	$127.8026	$127.80	$127.80	$127.80
Purchase #4	$123.27	6.427%	$131.1926	$131.19	$131.20	$131.20
Purchase #5	$214.60	12.868%	$242.2147	$242.21	$242.20	$242.20
Purchase #6	$137.67	7.532%	$148.0393	$148.04	$148.05	$148.00
Purchase #7	$162.87	10.720%	$180.3297	$180.33	$180.35	$180.30
7 purchase totals =	$1,060.17		$1,171.8516	$1,171.84	$1,171.85	$1,171.80