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	$31.68	6.238%	$33.6562	$33.66	$33.65	$33.70
Purchase #2	$93.49	4.681%	$97.8663	$97.87	$97.85	$97.90
Purchase #3	$206.83	7.835%	$223.0351	$223.04	$223.05	$223.00
Purchase #4	$226.81	12.688%	$255.5877	$255.59	$255.60	$255.60
Purchase #5	$149.85	5.816%	$158.5653	$158.57	$158.55	$158.60
Purchase #6	$203.72	8.861%	$221.7716	$221.77	$221.75	$221.80
Purchase #7	$50.79	13.223%	$57.506	$57.51	$57.50	$57.50
7 purchase totals =	$963.17		$1,047.9882	$1,048.01	$1,047.95	$1,048.10