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	$242.59	11.412%	$270.2744	$270.27	$270.25	$270.30
Purchase #2	$47.92	10.474%	$52.9391	$52.94	$52.95	$52.90
Purchase #3	$14.30	4.464%	$14.9384	$14.94	$14.95	$14.90
Purchase #4	$229.29	10.274%	$252.8473	$252.85	$252.85	$252.80
Purchase #5	$123.98	6.151%	$131.606	$131.61	$131.60	$131.60
Purchase #6	$208.77	10.844%	$231.409	$231.41	$231.40	$231.40
Purchase #7	$60.25	9.352%	$65.8846	$65.88	$65.90	$65.90
7 purchase totals =	$927.10		$1,019.8988	$1,019.90	$1,019.90	$1,019.80