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	$100.99	13.526%	$114.6499	$114.65	$114.65	$114.60
Purchase #2	$79.90	12.348%	$89.7661	$89.77	$89.75	$89.80
Purchase #3	$84.35	9.612%	$92.4577	$92.46	$92.45	$92.50
Purchase #4	$221.28	10.504%	$244.5233	$244.52	$244.50	$244.50
Purchase #5	$18.40	3.410%	$19.0274	$19.03	$19.05	$19.00
Purchase #6	$45.57	11.333%	$50.7344	$50.73	$50.75	$50.70
Purchase #7	$57.32	8.174%	$62.0053	$62.01	$62.00	$62.00
7 purchase totals =	$607.81		$673.1641	$673.17	$673.15	$673.10