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	$211.26	7.286%	$226.6524	$226.65	$226.65	$226.70
Purchase #2	$35.92	13.371%	$40.7229	$40.72	$40.70	$40.70
Purchase #3	$95.68	5.241%	$100.6946	$100.69	$100.70	$100.70
Purchase #4	$110.75	8.189%	$119.8193	$119.82	$119.80	$119.80
Purchase #5	$70.82	9.489%	$77.5401	$77.54	$77.55	$77.50
Purchase #6	$87.51	13.478%	$99.3046	$99.30	$99.30	$99.30
Purchase #7	$246.65	11.556%	$275.1529	$275.15	$275.15	$275.20
7 purchase totals =	$858.59		$939.8868	$939.87	$939.85	$939.90