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	$73.61	6.641%	$78.4984	$78.50	$78.50	$78.50
Purchase #2	$129.86	9.223%	$141.837	$141.84	$141.85	$141.80
Purchase #3	$223.43	10.486%	$246.8589	$246.86	$246.85	$246.90
Purchase #4	$10.92	11.849%	$12.2139	$12.21	$12.20	$12.20
Purchase #5	$164.55	9.288%	$179.8334	$179.83	$179.85	$179.80
Purchase #6	$227.71	9.759%	$249.9322	$249.93	$249.95	$249.90
Purchase #7	$247.85	10.687%	$274.3377	$274.34	$274.35	$274.30
7 purchase totals =	$1,077.93		$1,183.5115	$1,183.51	$1,183.55	$1,183.40