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	$29.96	10.481%	$33.1001	$33.10	$33.10	$33.10
Purchase #2	$205.96	7.682%	$221.7818	$221.78	$221.80	$221.80
Purchase #3	$39.47	3.124%	$40.703	$40.70	$40.70	$40.70
Purchase #4	$138.29	5.525%	$145.9305	$145.93	$145.95	$145.90
Purchase #5	$217.66	12.524%	$244.9197	$244.92	$244.90	$244.90
Purchase #6	$35.83	7.599%	$38.5527	$38.55	$38.55	$38.60
Purchase #7	$54.84	7.745%	$59.0874	$59.09	$59.10	$59.10
7 purchase totals =	$722.01		$784.0752	$784.07	$784.10	$784.10