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	$23.79	11.373%	$26.4956	$26.50	$26.50	$26.50
Purchase #2	$144.81	13.486%	$164.3391	$164.34	$164.35	$164.30
Purchase #3	$122.79	9.423%	$134.3605	$134.36	$134.35	$134.40
Purchase #4	$13.36	7.820%	$14.4048	$14.40	$14.40	$14.40
Purchase #5	$205.57	13.369%	$233.0527	$233.05	$233.05	$233.10
Purchase #6	$228.90	11.658%	$255.5852	$255.59	$255.60	$255.60
Purchase #7	$158.42	4.518%	$165.5774	$165.58	$165.60	$165.60
7 purchase totals =	$897.64		$993.8153	$993.82	$993.85	$993.90