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	$136.47	6.282%	$145.043	$145.04	$145.05	$145.00
Purchase #2	$39.31	3.400%	$40.6465	$40.65	$40.65	$40.60
Purchase #3	$44.96	12.178%	$50.4352	$50.44	$50.45	$50.40
Purchase #4	$229.71	3.488%	$237.7223	$237.72	$237.70	$237.70
Purchase #5	$86.89	4.341%	$90.6619	$90.66	$90.65	$90.70
Purchase #6	$105.71	5.124%	$111.1266	$111.13	$111.15	$111.10
Purchase #7	$20.63	12.523%	$23.2135	$23.21	$23.20	$23.20
7 purchase totals =	$663.68		$698.8490	$698.85	$698.85	$698.70