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	$64.65	4.225%	$67.3815	$67.38	$67.40	$67.40
Purchase #2	$52.37	9.731%	$57.4661	$57.47	$57.45	$57.50
Purchase #3	$248.79	12.464%	$279.7992	$279.80	$279.80	$279.80
Purchase #4	$174.97	12.404%	$196.6733	$196.67	$196.65	$196.70
Purchase #5	$56.52	6.775%	$60.3492	$60.35	$60.35	$60.30
Purchase #6	$72.75	7.669%	$78.3292	$78.33	$78.35	$78.30
Purchase #7	$177.88	7.114%	$190.5344	$190.53	$190.55	$190.50
7 purchase totals =	$847.93		$930.5329	$930.53	$930.55	$930.50