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	$34.72	13.139%	$39.2819	$39.28	$39.30	$39.30
Purchase #2	$173.30	3.544%	$179.4418	$179.44	$179.45	$179.40
Purchase #3	$237.57	3.530%	$245.9562	$245.96	$245.95	$246.00
Purchase #4	$189.52	12.843%	$213.8601	$213.86	$213.85	$213.90
Purchase #5	$179.35	9.748%	$196.833	$196.83	$196.85	$196.80
Purchase #6	$112.71	3.395%	$116.5365	$116.54	$116.55	$116.50
Purchase #7	$120.59	11.402%	$134.3397	$134.34	$134.35	$134.30
7 purchase totals =	$1,047.76		$1,126.2492	$1,126.25	$1,126.30	$1,126.20