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	$120.99	9.402%	$132.3655	$132.37	$132.35	$132.40
Purchase #2	$64.61	10.612%	$71.4664	$71.47	$71.45	$71.50
Purchase #3	$229.99	12.310%	$258.3018	$258.30	$258.30	$258.30
Purchase #4	$115.55	7.187%	$123.8546	$123.85	$123.85	$123.90
Purchase #5	$116.31	9.818%	$127.7293	$127.73	$127.75	$127.70
Purchase #6	$160.57	13.210%	$181.7813	$181.78	$181.80	$181.80
Purchase #7	$101.93	5.835%	$107.8776	$107.88	$107.90	$107.90
7 purchase totals =	$909.95		$1,003.3765	$1,003.38	$1,003.40	$1,003.50