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	$19.75	3.186%	$20.3792	$20.38	$20.40	$20.40
Purchase #2	$151.49	6.729%	$161.6838	$161.68	$161.70	$161.70
Purchase #3	$176.74	4.519%	$184.7269	$184.73	$184.75	$184.70
Purchase #4	$82.29	10.457%	$90.8951	$90.90	$90.90	$90.90
Purchase #5	$51.71	11.274%	$57.5398	$57.54	$57.55	$57.50
Purchase #6	$175.89	3.116%	$181.3707	$181.37	$181.35	$181.40
Purchase #7	$109.28	13.834%	$124.3978	$124.40	$124.40	$124.40
7 purchase totals =	$767.15		$820.9933	$821.00	$821.05	$821.00