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	$62.44	3.744%	$64.7778	$64.78	$64.80	$64.80
Purchase #2	$77.46	5.410%	$81.6506	$81.65	$81.65	$81.70
Purchase #3	$160.33	7.336%	$172.0918	$172.09	$172.10	$172.10
Purchase #4	$200.98	13.368%	$227.847	$227.85	$227.85	$227.80
Purchase #5	$78.38	13.697%	$89.1157	$89.12	$89.10	$89.10
Purchase #6	$119.99	3.228%	$123.8633	$123.86	$123.85	$123.90
Purchase #7	$195.90	11.320%	$218.0759	$218.08	$218.10	$218.10
7 purchase totals =	$895.48		$977.4221	$977.43	$977.45	$977.50