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	$119.52	6.730%	$127.5637	$127.56	$127.55	$127.60
Purchase #2	$80.59	4.368%	$84.1102	$84.11	$84.10	$84.10
Purchase #3	$35.94	12.827%	$40.55	$40.55	$40.55	$40.60
Purchase #4	$101.77	9.838%	$111.7821	$111.78	$111.80	$111.80
Purchase #5	$67.44	6.698%	$71.9571	$71.96	$71.95	$72.00
Purchase #6	$40.98	9.482%	$44.8657	$44.87	$44.85	$44.90
Purchase #7	$58.48	13.332%	$66.2766	$66.28	$66.30	$66.30
7 purchase totals =	$504.72		$547.1054	$547.11	$547.10	$547.30