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	$44.38	12.819%	$50.0691	$50.07	$50.05	$50.10
Purchase #2	$130.85	9.306%	$143.0269	$143.03	$143.05	$143.00
Purchase #3	$244.46	7.555%	$262.929	$262.93	$262.95	$262.90
Purchase #4	$164.58	4.601%	$172.1523	$172.15	$172.15	$172.20
Purchase #5	$67.51	7.696%	$72.7056	$72.71	$72.70	$72.70
Purchase #6	$82.38	4.591%	$86.1621	$86.16	$86.15	$86.20
Purchase #7	$27.75	13.745%	$31.5642	$31.56	$31.55	$31.60
7 purchase totals =	$761.91		$818.6092	$818.61	$818.60	$818.70