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	$53.96	4.768%	$56.5328	$56.53	$56.55	$56.50
Purchase #2	$157.28	7.119%	$168.4768	$168.48	$168.50	$168.50
Purchase #3	$86.53	3.118%	$89.228	$89.23	$89.25	$89.20
Purchase #4	$71.91	9.370%	$78.648	$78.65	$78.65	$78.60
Purchase #5	$173.35	8.398%	$187.9079	$187.91	$187.90	$187.90
Purchase #6	$106.49	4.279%	$111.0467	$111.05	$111.05	$111.00
Purchase #7	$76.29	12.724%	$85.9971	$86.00	$86.00	$86.00
7 purchase totals =	$725.81		$777.8373	$777.85	$777.90	$777.70