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	$204.51	9.737%	$224.4231	$224.42	$224.40	$224.40
Purchase #2	$86.56	10.405%	$95.5666	$95.57	$95.55	$95.60
Purchase #3	$74.75	10.177%	$82.3573	$82.36	$82.35	$82.40
Purchase #4	$72.89	7.543%	$78.3881	$78.39	$78.40	$78.40
Purchase #5	$29.73	5.796%	$31.4532	$31.45	$31.45	$31.50
Purchase #6	$70.82	3.597%	$73.3674	$73.37	$73.35	$73.40
Purchase #7	$38.44	9.344%	$42.0318	$42.03	$42.05	$42.00
7 purchase totals =	$577.70		$627.5875	$627.59	$627.55	$627.70