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	$83.57	8.469%	$90.6475	$90.65	$90.65	$90.60
Purchase #2	$151.87	12.568%	$170.957	$170.96	$170.95	$171.00
Purchase #3	$136.81	10.656%	$151.3885	$151.39	$151.40	$151.40
Purchase #4	$232.41	6.268%	$246.9775	$246.98	$247.00	$247.00
Purchase #5	$15.71	11.294%	$17.4843	$17.48	$17.50	$17.50
Purchase #6	$231.65	10.489%	$255.9478	$255.95	$255.95	$255.90
Purchase #7	$99.45	9.680%	$109.0768	$109.08	$109.10	$109.10
7 purchase totals =	$951.47		$1,042.4794	$1,042.49	$1,042.55	$1,042.50