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	$81.91	3.276%	$84.5934	$84.59	$84.60	$84.60
Purchase #2	$179.58	8.605%	$195.0329	$195.03	$195.05	$195.00
Purchase #3	$123.54	3.499%	$127.8627	$127.86	$127.85	$127.90
Purchase #4	$59.83	12.842%	$67.5134	$67.51	$67.50	$67.50
Purchase #5	$76.51	11.851%	$85.5772	$85.58	$85.60	$85.60
Purchase #6	$38.70	4.277%	$40.3552	$40.36	$40.35	$40.40
Purchase #7	$122.83	10.274%	$135.4496	$135.45	$135.45	$135.40
7 purchase totals =	$682.90		$736.3844	$736.38	$736.40	$736.40