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	$135.47	4.551%	$141.6352	$141.64	$141.65	$141.60
Purchase #2	$40.93	8.799%	$44.5314	$44.53	$44.55	$44.50
Purchase #3	$186.35	5.311%	$196.247	$196.25	$196.25	$196.20
Purchase #4	$131.60	9.603%	$144.2375	$144.24	$144.25	$144.20
Purchase #5	$44.33	3.480%	$45.8727	$45.87	$45.85	$45.90
Purchase #6	$122.82	11.449%	$136.8817	$136.88	$136.90	$136.90
Purchase #7	$88.43	7.696%	$95.2356	$95.24	$95.25	$95.20
7 purchase totals =	$749.93		$804.6411	$804.65	$804.70	$804.50