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	$109.97	4.212%	$114.6019	$114.60	$114.60	$114.60
Purchase #2	$143.29	8.597%	$155.6086	$155.61	$155.60	$155.60
Purchase #3	$97.92	6.724%	$104.5041	$104.50	$104.50	$104.50
Purchase #4	$140.76	13.718%	$160.0695	$160.07	$160.05	$160.10
Purchase #5	$216.31	7.187%	$231.8562	$231.86	$231.85	$231.90
Purchase #6	$131.99	3.116%	$136.1028	$136.10	$136.10	$136.10
Purchase #7	$17.54	5.337%	$18.4761	$18.48	$18.50	$18.50
7 purchase totals =	$857.78		$921.2192	$921.22	$921.20	$921.30