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	$84.82	10.498%	$93.7244	$93.72	$93.70	$93.70
Purchase #2	$196.26	12.846%	$221.4716	$221.47	$221.45	$221.50
Purchase #3	$100.39	13.501%	$113.9437	$113.94	$113.95	$113.90
Purchase #4	$193.77	8.800%	$210.8218	$210.82	$210.80	$210.80
Purchase #5	$117.30	12.172%	$131.5778	$131.58	$131.60	$131.60
Purchase #6	$39.70	5.403%	$41.845	$41.85	$41.85	$41.80
Purchase #7	$38.72	12.625%	$43.6084	$43.61	$43.60	$43.60
7 purchase totals =	$770.96		$856.9927	$856.99	$856.95	$856.90