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	$243.82	4.745%	$255.3893	$255.39	$255.40	$255.40
Purchase #2	$85.86	3.469%	$88.8385	$88.84	$88.85	$88.80
Purchase #3	$211.86	12.655%	$238.6709	$238.67	$238.65	$238.70
Purchase #4	$17.50	13.779%	$19.9113	$19.91	$19.90	$19.90
Purchase #5	$20.67	3.558%	$21.4054	$21.41	$21.40	$21.40
Purchase #6	$188.45	5.307%	$198.451	$198.45	$198.45	$198.50
Purchase #7	$15.88	3.471%	$16.4312	$16.43	$16.45	$16.40
7 purchase totals =	$784.04		$839.0976	$839.10	$839.10	$839.10