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	$51.72	13.218%	$58.5563	$58.56	$58.55	$58.60
Purchase #2	$19.65	9.188%	$21.4554	$21.46	$21.45	$21.50
Purchase #3	$50.26	12.415%	$56.4998	$56.50	$56.50	$56.50
Purchase #4	$87.56	3.614%	$90.7244	$90.72	$90.70	$90.70
Purchase #5	$161.50	9.639%	$177.067	$177.07	$177.05	$177.10
Purchase #6	$82.45	11.533%	$91.959	$91.96	$91.95	$92.00
Purchase #7	$55.50	13.266%	$62.8626	$62.86	$62.85	$62.90
7 purchase totals =	$508.64		$559.1245	$559.13	$559.05	$559.30