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	$226.28	8.501%	$245.5161	$245.52	$245.50	$245.50
Purchase #2	$86.99	11.393%	$96.9008	$96.90	$96.90	$96.90
Purchase #3	$73.64	9.366%	$80.5371	$80.54	$80.55	$80.50
Purchase #4	$227.88	5.489%	$240.3883	$240.39	$240.40	$240.40
Purchase #5	$200.38	7.590%	$215.5888	$215.59	$215.60	$215.60
Purchase #6	$208.93	10.606%	$231.0891	$231.09	$231.10	$231.10
Purchase #7	$116.71	12.652%	$131.4761	$131.48	$131.50	$131.50
7 purchase totals =	$1,140.81		$1,241.4963	$1,241.51	$1,241.55	$1,241.50