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	$12.58	10.619%	$13.9159	$13.92	$13.90	$13.90
Purchase #2	$144.69	3.204%	$149.3259	$149.33	$149.35	$149.30
Purchase #3	$202.44	11.317%	$225.3501	$225.35	$225.35	$225.40
Purchase #4	$56.33	5.267%	$59.2969	$59.30	$59.30	$59.30
Purchase #5	$70.57	3.180%	$72.8141	$72.81	$72.80	$72.80
Purchase #6	$150.33	7.551%	$161.6814	$161.68	$161.70	$161.70
Purchase #7	$248.65	12.789%	$280.4498	$280.45	$280.45	$280.40
7 purchase totals =	$885.59		$962.8341	$962.84	$962.85	$962.80