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	$53.47	6.523%	$56.9578	$56.96	$56.95	$57.00
Purchase #2	$185.72	10.785%	$205.7499	$205.75	$205.75	$205.70
Purchase #3	$138.47	4.188%	$144.2691	$144.27	$144.25	$144.30
Purchase #4	$99.25	6.475%	$105.6764	$105.68	$105.70	$105.70
Purchase #5	$231.98	5.641%	$245.066	$245.07	$245.05	$245.10
Purchase #6	$32.67	11.333%	$36.3725	$36.37	$36.35	$36.40
Purchase #7	$209.37	8.800%	$227.7946	$227.79	$227.80	$227.80
7 purchase totals =	$950.93		$1,021.8863	$1,021.89	$1,021.85	$1,022.00