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	$75.40	4.236%	$78.5939	$78.59	$78.60	$78.60
Purchase #2	$214.31	12.705%	$241.5381	$241.54	$241.55	$241.50
Purchase #3	$77.89	13.172%	$88.1497	$88.15	$88.15	$88.10
Purchase #4	$190.71	13.191%	$215.8666	$215.87	$215.85	$215.90
Purchase #5	$31.43	8.834%	$34.2065	$34.21	$34.20	$34.20
Purchase #6	$243.54	8.385%	$263.9608	$263.96	$263.95	$264.00
Purchase #7	$177.79	10.523%	$196.4988	$196.50	$196.50	$196.50
7 purchase totals =	$1,011.07		$1,118.8144	$1,118.82	$1,118.80	$1,118.80