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	$40.95	5.534%	$43.2162	$43.22	$43.20	$43.20
Purchase #2	$34.42	12.174%	$38.6103	$38.61	$38.60	$38.60
Purchase #3	$133.42	6.730%	$142.3992	$142.40	$142.40	$142.40
Purchase #4	$224.94	7.650%	$242.1479	$242.15	$242.15	$242.10
Purchase #5	$229.57	8.813%	$249.802	$249.80	$249.80	$249.80
Purchase #6	$94.92	7.358%	$101.9042	$101.90	$101.90	$101.90
Purchase #7	$101.67	3.389%	$105.1156	$105.12	$105.10	$105.10
7 purchase totals =	$859.89		$923.1954	$923.20	$923.15	$923.10