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	$37.88	13.157%	$42.8639	$42.86	$42.85	$42.90
Purchase #2	$11.37	9.270%	$12.424	$12.42	$12.40	$12.40
Purchase #3	$70.82	13.476%	$80.3637	$80.36	$80.35	$80.40
Purchase #4	$18.26	5.554%	$19.2742	$19.27	$19.25	$19.30
Purchase #5	$116.31	12.154%	$130.4463	$130.45	$130.45	$130.40
Purchase #6	$168.54	10.512%	$186.2569	$186.26	$186.25	$186.30
Purchase #7	$186.82	5.342%	$196.7999	$196.80	$196.80	$196.80
7 purchase totals =	$610.00		$668.4289	$668.42	$668.35	$668.50