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	$128.43	9.459%	$140.5782	$140.58	$140.60	$140.60
Purchase #2	$127.94	10.126%	$140.8952	$140.90	$140.90	$140.90
Purchase #3	$188.98	10.355%	$208.5489	$208.55	$208.55	$208.50
Purchase #4	$63.40	6.866%	$67.753	$67.75	$67.75	$67.80
Purchase #5	$232.43	5.812%	$245.9388	$245.94	$245.95	$245.90
Purchase #6	$181.63	8.254%	$196.6217	$196.62	$196.60	$196.60
Purchase #7	$181.28	4.516%	$189.4666	$189.47	$189.45	$189.50
7 purchase totals =	$1,104.09		$1,189.8024	$1,189.81	$1,189.80	$1,189.80