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	$65.36	12.792%	$73.7209	$73.72	$73.70	$73.70
Purchase #2	$83.68	7.405%	$89.8765	$89.88	$89.90	$89.90
Purchase #3	$45.58	11.661%	$50.8951	$50.90	$50.90	$50.90
Purchase #4	$38.84	9.248%	$42.4319	$42.43	$42.45	$42.40
Purchase #5	$129.47	12.575%	$145.7509	$145.75	$145.75	$145.80
Purchase #6	$12.43	8.224%	$13.4522	$13.45	$13.45	$13.50
Purchase #7	$12.83	4.477%	$13.4044	$13.40	$13.40	$13.40
7 purchase totals =	$388.19		$429.5319	$429.53	$429.55	$429.60