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	$129.71	7.557%	$139.5122	$139.51	$139.50	$139.50
Purchase #2	$28.58	9.584%	$31.3191	$31.32	$31.30	$31.30
Purchase #3	$58.75	13.785%	$66.8487	$66.85	$66.85	$66.80
Purchase #4	$238.47	7.120%	$255.4491	$255.45	$255.45	$255.40
Purchase #5	$11.73	12.725%	$13.2226	$13.22	$13.20	$13.20
Purchase #6	$158.95	8.133%	$171.8774	$171.88	$171.90	$171.90
Purchase #7	$245.86	9.235%	$268.5652	$268.57	$268.55	$268.60
7 purchase totals =	$872.05		$946.7943	$946.80	$946.75	$946.70