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	$167.41	10.432%	$184.8742	$184.87	$184.85	$184.90
Purchase #2	$233.79	4.585%	$244.5093	$244.51	$244.50	$244.50
Purchase #3	$227.67	7.105%	$243.846	$243.85	$243.85	$243.80
Purchase #4	$29.47	10.389%	$32.5316	$32.53	$32.55	$32.50
Purchase #5	$131.25	9.622%	$143.8789	$143.88	$143.90	$143.90
Purchase #6	$18.75	13.464%	$21.2745	$21.27	$21.25	$21.30
Purchase #7	$123.34	10.202%	$135.9231	$135.92	$135.90	$135.90
7 purchase totals =	$931.68		$1,006.8376	$1,006.83	$1,006.80	$1,006.80