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	$72.34	13.640%	$82.2072	$82.21	$82.20	$82.20
Purchase #2	$132.81	13.302%	$150.4764	$150.48	$150.50	$150.50
Purchase #3	$10.73	6.428%	$11.4197	$11.42	$11.40	$11.40
Purchase #4	$185.82	13.335%	$210.5991	$210.60	$210.60	$210.60
Purchase #5	$104.31	9.128%	$113.8314	$113.83	$113.85	$113.80
Purchase #6	$24.38	13.387%	$27.6438	$27.64	$27.65	$27.60
Purchase #7	$133.37	7.116%	$142.8606	$142.86	$142.85	$142.90
7 purchase totals =	$663.76		$739.0382	$739.04	$739.05	$739.00