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	$119.52	10.288%	$131.8162	$131.82	$131.80	$131.80
Purchase #2	$231.74	7.765%	$249.7346	$249.73	$249.75	$249.70
Purchase #3	$24.73	12.792%	$27.8935	$27.89	$27.90	$27.90
Purchase #4	$58.68	13.496%	$66.5995	$66.60	$66.60	$66.60
Purchase #5	$169.49	9.536%	$185.6526	$185.65	$185.65	$185.70
Purchase #6	$10.96	5.329%	$11.5441	$11.54	$11.55	$11.50
Purchase #7	$50.97	10.511%	$56.3275	$56.33	$56.35	$56.30
7 purchase totals =	$666.09		$729.5680	$729.56	$729.60	$729.50