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	$80.39	6.405%	$85.539	$85.54	$85.55	$85.50
Purchase #2	$194.36	12.852%	$219.3391	$219.34	$219.35	$219.30
Purchase #3	$28.47	4.180%	$29.66	$29.66	$29.65	$29.70
Purchase #4	$41.89	13.269%	$47.4484	$47.45	$47.45	$47.40
Purchase #5	$156.55	3.408%	$161.8852	$161.89	$161.90	$161.90
Purchase #6	$124.88	13.277%	$141.4603	$141.46	$141.45	$141.50
Purchase #7	$249.82	8.823%	$271.8616	$271.86	$271.85	$271.90
7 purchase totals =	$876.36		$957.1936	$957.20	$957.20	$957.20