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	$10.91	13.768%	$12.4121	$12.41	$12.40	$12.40
Purchase #2	$67.64	4.168%	$70.4592	$70.46	$70.45	$70.50
Purchase #3	$226.47	12.283%	$254.2873	$254.29	$254.30	$254.30
Purchase #4	$59.40	11.789%	$66.4027	$66.40	$66.40	$66.40
Purchase #5	$215.68	11.698%	$240.9102	$240.91	$240.90	$240.90
Purchase #6	$39.35	8.173%	$42.5661	$42.57	$42.55	$42.60
Purchase #7	$206.29	10.244%	$227.4223	$227.42	$227.40	$227.40
7 purchase totals =	$825.74		$914.4599	$914.46	$914.40	$914.50