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	$109.88	8.550%	$119.2747	$119.27	$119.25	$119.30
Purchase #2	$164.80	7.241%	$176.7332	$176.73	$176.75	$176.70
Purchase #3	$226.40	5.519%	$238.895	$238.90	$238.90	$238.90
Purchase #4	$50.37	4.693%	$52.7339	$52.73	$52.75	$52.70
Purchase #5	$40.79	12.619%	$45.9373	$45.94	$45.95	$45.90
Purchase #6	$218.35	5.326%	$229.9793	$229.98	$230.00	$230.00
Purchase #7	$130.65	6.767%	$139.4911	$139.49	$139.50	$139.50
7 purchase totals =	$941.24		$1,003.0445	$1,003.04	$1,003.10	$1,003.00