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	$119.31	13.571%	$135.5016	$135.50	$135.50	$135.50
Purchase #2	$151.42	6.186%	$160.7868	$160.79	$160.80	$160.80
Purchase #3	$88.93	12.316%	$99.8826	$99.88	$99.90	$99.90
Purchase #4	$189.55	13.380%	$214.9118	$214.91	$214.90	$214.90
Purchase #5	$140.67	7.724%	$151.5354	$151.54	$151.55	$151.50
Purchase #6	$10.84	3.602%	$11.2305	$11.23	$11.25	$11.20
Purchase #7	$174.29	12.458%	$196.003	$196.00	$196.00	$196.00
7 purchase totals =	$875.01		$969.8517	$969.85	$969.90	$969.80