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	$108.27	3.615%	$112.184	$112.18	$112.20	$112.20
Purchase #2	$115.95	13.270%	$131.3366	$131.34	$131.35	$131.30
Purchase #3	$78.50	9.382%	$85.8649	$85.86	$85.85	$85.90
Purchase #4	$52.81	13.337%	$59.8533	$59.85	$59.85	$59.90
Purchase #5	$39.68	6.776%	$42.3687	$42.37	$42.35	$42.40
Purchase #6	$20.31	11.176%	$22.5798	$22.58	$22.60	$22.60
Purchase #7	$183.57	5.236%	$193.1817	$193.18	$193.20	$193.20
7 purchase totals =	$599.09		$647.3690	$647.36	$647.40	$647.50