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	$75.80	3.581%	$78.5144	$78.51	$78.50	$78.50
Purchase #2	$227.56	4.229%	$237.1835	$237.18	$237.20	$237.20
Purchase #3	$50.54	8.553%	$54.8627	$54.86	$54.85	$54.90
Purchase #4	$229.79	12.700%	$258.9733	$258.97	$258.95	$259.00
Purchase #5	$228.71	7.653%	$246.2132	$246.21	$246.20	$246.20
Purchase #6	$131.54	11.309%	$146.4159	$146.42	$146.40	$146.40
Purchase #7	$141.96	10.849%	$157.3612	$157.36	$157.35	$157.40
7 purchase totals =	$1,085.90		$1,179.5242	$1,179.51	$1,179.45	$1,179.60