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	$139.31	8.256%	$150.8114	$150.81	$150.80	$150.80
Purchase #2	$215.73	12.159%	$241.9606	$241.96	$241.95	$242.00
Purchase #3	$225.38	7.186%	$241.5758	$241.58	$241.60	$241.60
Purchase #4	$154.90	6.319%	$164.6881	$164.69	$164.70	$164.70
Purchase #5	$238.74	6.815%	$255.0101	$255.01	$255.00	$255.00
Purchase #6	$195.71	4.173%	$203.877	$203.88	$203.90	$203.90
Purchase #7	$168.39	10.329%	$185.783	$185.78	$185.80	$185.80
7 purchase totals =	$1,338.16		$1,443.7060	$1,443.71	$1,443.75	$1,443.80