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	$54.57	8.787%	$59.3651	$59.37	$59.35	$59.40
Purchase #2	$35.67	10.738%	$39.5002	$39.50	$39.50	$39.50
Purchase #3	$46.54	9.764%	$51.0842	$51.08	$51.10	$51.10
Purchase #4	$142.46	4.403%	$148.7325	$148.73	$148.75	$148.70
Purchase #5	$61.95	10.553%	$68.4876	$68.49	$68.50	$68.50
Purchase #6	$94.80	10.133%	$104.4061	$104.41	$104.40	$104.40
Purchase #7	$96.47	12.538%	$108.5654	$108.57	$108.55	$108.60
7 purchase totals =	$532.46		$580.1411	$580.15	$580.15	$580.20