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	$82.62	6.622%	$88.0911	$88.09	$88.10	$88.10
Purchase #2	$226.84	6.254%	$241.0266	$241.03	$241.05	$241.00
Purchase #3	$223.74	7.734%	$241.0441	$241.04	$241.05	$241.00
Purchase #4	$43.95	6.496%	$46.805	$46.81	$46.80	$46.80
Purchase #5	$71.96	9.111%	$78.5163	$78.52	$78.50	$78.50
Purchase #6	$70.31	8.861%	$76.5402	$76.54	$76.55	$76.50
Purchase #7	$91.46	7.307%	$98.143	$98.14	$98.15	$98.10
7 purchase totals =	$810.88		$870.1663	$870.17	$870.20	$870.00