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	$82.54	8.873%	$89.8638	$89.86	$89.85	$89.90
Purchase #2	$200.25	3.176%	$206.6099	$206.61	$206.60	$206.60
Purchase #3	$250.47	3.665%	$259.6497	$259.65	$259.65	$259.60
Purchase #4	$33.91	4.605%	$35.4716	$35.47	$35.45	$35.50
Purchase #5	$173.38	9.276%	$189.4627	$189.46	$189.45	$189.50
Purchase #6	$247.72	11.392%	$275.9403	$275.94	$275.95	$275.90
Purchase #7	$52.98	8.265%	$57.3588	$57.36	$57.35	$57.40
7 purchase totals =	$1,041.25		$1,114.3568	$1,114.35	$1,114.30	$1,114.40