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	$102.42	10.229%	$112.8965	$112.90	$112.90	$112.90
Purchase #2	$187.48	4.720%	$196.3291	$196.33	$196.35	$196.30
Purchase #3	$108.99	13.178%	$123.3527	$123.35	$123.35	$123.40
Purchase #4	$74.49	7.429%	$80.0239	$80.02	$80.00	$80.00
Purchase #5	$42.46	5.551%	$44.817	$44.82	$44.80	$44.80
Purchase #6	$21.63	12.436%	$24.3199	$24.32	$24.30	$24.30
Purchase #7	$220.56	12.197%	$247.4617	$247.46	$247.45	$247.50
7 purchase totals =	$758.03		$829.2008	$829.20	$829.15	$829.20