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	$11.61	11.172%	$12.9071	$12.91	$12.90	$12.90
Purchase #2	$147.31	5.245%	$155.0364	$155.04	$155.05	$155.00
Purchase #3	$165.69	8.605%	$179.9476	$179.95	$179.95	$179.90
Purchase #4	$22.93	9.480%	$25.1038	$25.10	$25.10	$25.10
Purchase #5	$56.28	9.254%	$61.4882	$61.49	$61.50	$61.50
Purchase #6	$36.73	10.770%	$40.6858	$40.69	$40.70	$40.70
Purchase #7	$55.60	6.848%	$59.4075	$59.41	$59.40	$59.40
7 purchase totals =	$496.15		$534.5764	$534.59	$534.60	$534.50