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	$41.74	13.457%	$47.357	$47.36	$47.35	$47.40
Purchase #2	$16.87	8.862%	$18.365	$18.37	$18.35	$18.40
Purchase #3	$137.27	11.250%	$152.7129	$152.71	$152.70	$152.70
Purchase #4	$144.72	4.577%	$151.3438	$151.34	$151.35	$151.30
Purchase #5	$47.37	8.846%	$51.5604	$51.56	$51.55	$51.60
Purchase #6	$38.94	10.189%	$42.9076	$42.91	$42.90	$42.90
Purchase #7	$186.28	6.587%	$198.5503	$198.55	$198.55	$198.60
7 purchase totals =	$613.19		$662.7970	$662.80	$662.75	$662.90