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	$59.28	12.779%	$66.8554	$66.86	$66.85	$66.90
Purchase #2	$100.43	10.152%	$110.6257	$110.63	$110.65	$110.60
Purchase #3	$149.83	11.826%	$167.5489	$167.55	$167.55	$167.50
Purchase #4	$228.59	12.751%	$257.7375	$257.74	$257.75	$257.70
Purchase #5	$123.28	13.811%	$140.3062	$140.31	$140.30	$140.30
Purchase #6	$72.82	5.683%	$76.9584	$76.96	$76.95	$77.00
Purchase #7	$82.25	8.712%	$89.4156	$89.42	$89.40	$89.40
7 purchase totals =	$816.48		$909.4477	$909.47	$909.45	$909.40