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	$238.35	13.865%	$271.3972	$271.40	$271.40	$271.40
Purchase #2	$50.69	5.683%	$53.5707	$53.57	$53.55	$53.60
Purchase #3	$113.53	12.671%	$127.9154	$127.92	$127.90	$127.90
Purchase #4	$187.38	4.614%	$196.0257	$196.03	$196.05	$196.00
Purchase #5	$123.99	5.766%	$131.1393	$131.14	$131.15	$131.10
Purchase #6	$61.52	6.319%	$65.4074	$65.41	$65.40	$65.40
Purchase #7	$22.95	10.483%	$25.3558	$25.36	$25.35	$25.40
7 purchase totals =	$798.41		$870.8115	$870.83	$870.80	$870.80