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	$37.31	5.351%	$39.3065	$39.31	$39.30	$39.30
Purchase #2	$48.96	4.445%	$51.1363	$51.14	$51.15	$51.10
Purchase #3	$59.54	13.358%	$67.4934	$67.49	$67.50	$67.50
Purchase #4	$222.85	10.544%	$246.3473	$246.35	$246.35	$246.30
Purchase #5	$87.49	10.599%	$96.7631	$96.76	$96.75	$96.80
Purchase #6	$187.29	3.324%	$193.5155	$193.52	$193.50	$193.50
Purchase #7	$249.45	10.153%	$274.7767	$274.78	$274.80	$274.80
7 purchase totals =	$892.89		$969.3388	$969.35	$969.35	$969.30