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	$126.52	12.725%	$142.6197	$142.62	$142.60	$142.60
Purchase #2	$200.35	12.563%	$225.52	$225.52	$225.50	$225.50
Purchase #3	$36.61	10.375%	$40.4083	$40.41	$40.40	$40.40
Purchase #4	$91.66	4.533%	$95.8149	$95.81	$95.80	$95.80
Purchase #5	$147.98	3.296%	$152.8574	$152.86	$152.85	$152.90
Purchase #6	$59.37	13.574%	$67.4289	$67.43	$67.45	$67.40
Purchase #7	$112.65	3.621%	$116.7291	$116.73	$116.75	$116.70
7 purchase totals =	$775.14		$841.3783	$841.38	$841.35	$841.30