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	$72.63	13.736%	$82.6065	$82.61	$82.60	$82.60
Purchase #2	$170.40	13.526%	$193.4483	$193.45	$193.45	$193.40
Purchase #3	$134.56	13.366%	$152.5453	$152.55	$152.55	$152.50
Purchase #4	$75.37	4.421%	$78.7021	$78.70	$78.70	$78.70
Purchase #5	$82.76	5.772%	$87.5369	$87.54	$87.55	$87.50
Purchase #6	$154.99	3.407%	$160.2705	$160.27	$160.25	$160.30
Purchase #7	$76.61	10.673%	$84.7866	$84.79	$84.80	$84.80
7 purchase totals =	$767.32		$839.8962	$839.91	$839.90	$839.80