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	$127.80	9.350%	$139.7493	$139.75	$139.75	$139.70
Purchase #2	$191.43	13.607%	$217.4779	$217.48	$217.50	$217.50
Purchase #3	$61.55	9.200%	$67.2126	$67.21	$67.20	$67.20
Purchase #4	$215.33	3.362%	$222.5694	$222.57	$222.55	$222.60
Purchase #5	$173.37	3.763%	$179.8939	$179.89	$179.90	$179.90
Purchase #6	$6.84	4.470%	$7.1457	$7.15	$7.15	$7.10
Purchase #7	$214.46	3.248%	$221.4257	$221.43	$221.45	$221.40
7 purchase totals =	$990.78		$1,055.4745	$1,055.48	$1,055.50	$1,055.40