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	$31.90	3.240%	$32.9336	$32.93	$32.95	$32.90
Purchase #2	$218.71	7.386%	$234.8639	$234.86	$234.85	$234.90
Purchase #3	$186.83	11.585%	$208.4743	$208.47	$208.45	$208.50
Purchase #4	$184.90	6.197%	$196.3583	$196.36	$196.35	$196.40
Purchase #5	$86.44	10.356%	$95.3917	$95.39	$95.40	$95.40
Purchase #6	$113.88	12.522%	$128.1401	$128.14	$128.15	$128.10
Purchase #7	$214.59	12.455%	$241.3172	$241.32	$241.30	$241.30
7 purchase totals =	$1,037.25		$1,137.4791	$1,137.47	$1,137.45	$1,137.50