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	$139.50	6.316%	$148.3108	$148.31	$148.30	$148.30
Purchase #2	$149.38	11.769%	$166.9605	$166.96	$166.95	$167.00
Purchase #3	$112.26	10.404%	$123.9395	$123.94	$123.95	$123.90
Purchase #4	$196.68	4.650%	$205.8256	$205.83	$205.85	$205.80
Purchase #5	$43.26	9.677%	$47.4463	$47.45	$47.45	$47.40
Purchase #6	$162.29	7.615%	$174.6484	$174.65	$174.65	$174.60
Purchase #7	$192.93	10.241%	$212.688	$212.69	$212.70	$212.70
7 purchase totals =	$996.30		$1,079.8191	$1,079.83	$1,079.85	$1,079.70