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	$19.45	11.715%	$21.7286	$21.73	$21.75	$21.70
Purchase #2	$149.26	8.687%	$162.2262	$162.23	$162.25	$162.20
Purchase #3	$62.96	7.576%	$67.7298	$67.73	$67.75	$67.70
Purchase #4	$32.74	11.693%	$36.5683	$36.57	$36.55	$36.60
Purchase #5	$50.94	7.373%	$54.6958	$54.70	$54.70	$54.70
Purchase #6	$25.54	7.127%	$27.3602	$27.36	$27.35	$27.40
Purchase #7	$153.46	5.730%	$162.2533	$162.25	$162.25	$162.30
7 purchase totals =	$494.35		$532.5622	$532.57	$532.60	$532.60