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	$51.70	8.567%	$56.1291	$56.13	$56.15	$56.10
Purchase #2	$190.84	13.186%	$216.0042	$216.00	$216.00	$216.00
Purchase #3	$48.43	7.758%	$52.1872	$52.19	$52.20	$52.20
Purchase #4	$78.50	13.482%	$89.0834	$89.08	$89.10	$89.10
Purchase #5	$5.73	11.830%	$6.4079	$6.41	$6.40	$6.40
Purchase #6	$200.94	12.239%	$225.533	$225.53	$225.55	$225.50
Purchase #7	$200.57	12.461%	$225.563	$225.56	$225.55	$225.60
7 purchase totals =	$776.71		$870.9078	$870.90	$870.95	$870.90