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	$146.58	12.345%	$164.6753	$164.68	$164.70	$164.70
Purchase #2	$70.25	11.553%	$78.366	$78.37	$78.35	$78.40
Purchase #3	$112.34	6.168%	$119.2691	$119.27	$119.25	$119.30
Purchase #4	$71.60	7.380%	$76.8841	$76.88	$76.90	$76.90
Purchase #5	$104.74	11.359%	$116.6374	$116.64	$116.65	$116.60
Purchase #6	$19.50	4.135%	$20.3063	$20.31	$20.30	$20.30
Purchase #7	$229.33	12.714%	$258.487	$258.49	$258.50	$258.50
7 purchase totals =	$754.34		$834.6252	$834.64	$834.65	$834.70