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	$29.82	5.660%	$31.5078	$31.51	$31.50	$31.50
Purchase #2	$130.44	8.311%	$141.2809	$141.28	$141.30	$141.30
Purchase #3	$170.25	5.473%	$179.5678	$179.57	$179.55	$179.60
Purchase #4	$116.32	6.221%	$123.5563	$123.56	$123.55	$123.60
Purchase #5	$235.83	9.474%	$258.1725	$258.17	$258.15	$258.20
Purchase #6	$113.44	7.504%	$121.9525	$121.95	$121.95	$122.00
Purchase #7	$231.80	9.327%	$253.42	$253.42	$253.40	$253.40
7 purchase totals =	$1,027.90		$1,109.4578	$1,109.46	$1,109.40	$1,109.60