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	$53.58	10.230%	$59.0612	$59.06	$59.05	$59.10
Purchase #2	$90.99	11.693%	$101.6295	$101.63	$101.65	$101.60
Purchase #3	$187.71	4.562%	$196.2733	$196.27	$196.25	$196.30
Purchase #4	$37.35	8.288%	$40.4456	$40.45	$40.45	$40.40
Purchase #5	$163.67	11.339%	$182.2285	$182.23	$182.25	$182.20
Purchase #6	$85.90	12.788%	$96.8849	$96.88	$96.90	$96.90
Purchase #7	$154.49	5.787%	$163.4303	$163.43	$163.45	$163.40
7 purchase totals =	$773.69		$839.9533	$839.95	$840.00	$839.90