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	$40.32	10.156%	$44.4149	$44.41	$44.40	$44.40
Purchase #2	$35.27	9.538%	$38.6341	$38.63	$38.65	$38.60
Purchase #3	$78.90	4.431%	$82.3961	$82.40	$82.40	$82.40
Purchase #4	$81.93	4.736%	$85.8102	$85.81	$85.80	$85.80
Purchase #5	$17.76	5.437%	$18.7256	$18.73	$18.75	$18.70
Purchase #6	$86.32	4.175%	$89.9239	$89.92	$89.90	$89.90
Purchase #7	$248.54	13.258%	$281.4914	$281.49	$281.50	$281.50
7 purchase totals =	$589.04		$641.3962	$641.39	$641.40	$641.30