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	$33.72	12.170%	$37.8237	$37.82	$37.80	$37.80
Purchase #2	$152.87	4.538%	$159.8072	$159.81	$159.80	$159.80
Purchase #3	$224.34	7.153%	$240.387	$240.39	$240.40	$240.40
Purchase #4	$239.25	12.310%	$268.7017	$268.70	$268.70	$268.70
Purchase #5	$196.59	12.711%	$221.5786	$221.58	$221.60	$221.60
Purchase #6	$153.39	13.305%	$173.7985	$173.80	$173.80	$173.80
Purchase #7	$176.66	12.375%	$198.5217	$198.52	$198.50	$198.50
7 purchase totals =	$1,176.82		$1,300.6184	$1,300.62	$1,300.60	$1,300.60