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	$135.48	3.182%	$139.791	$139.79	$139.80	$139.80
Purchase #2	$156.51	6.792%	$167.1402	$167.14	$167.15	$167.10
Purchase #3	$56.86	5.187%	$59.8093	$59.81	$59.80	$59.80
Purchase #4	$24.57	9.774%	$26.9715	$26.97	$26.95	$27.00
Purchase #5	$244.35	8.146%	$264.2548	$264.25	$264.25	$264.30
Purchase #6	$226.58	13.104%	$256.271	$256.27	$256.25	$256.30
Purchase #7	$90.33	12.862%	$101.9482	$101.95	$101.95	$101.90
7 purchase totals =	$934.68		$1,016.1860	$1,016.18	$1,016.15	$1,016.20