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	$69.87	12.373%	$78.515	$78.52	$78.50	$78.50
Purchase #2	$78.32	5.838%	$82.8923	$82.89	$82.90	$82.90
Purchase #3	$217.84	3.186%	$224.7804	$224.78	$224.80	$224.80
Purchase #4	$57.67	4.624%	$60.3367	$60.34	$60.35	$60.30
Purchase #5	$69.69	4.472%	$72.8065	$72.81	$72.80	$72.80
Purchase #6	$199.30	7.332%	$213.9127	$213.91	$213.90	$213.90
Purchase #7	$150.96	7.116%	$161.7023	$161.70	$161.70	$161.70
7 purchase totals =	$843.65		$894.9459	$894.95	$894.95	$894.90