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	$75.38	3.622%	$78.1103	$78.11	$78.10	$78.10
Purchase #2	$62.64	7.524%	$67.353	$67.35	$67.35	$67.40
Purchase #3	$108.57	12.508%	$122.1499	$122.15	$122.15	$122.10
Purchase #4	$138.32	8.469%	$150.0343	$150.03	$150.05	$150.00
Purchase #5	$60.54	11.506%	$67.5057	$67.51	$67.50	$67.50
Purchase #6	$145.67	6.330%	$154.8909	$154.89	$154.90	$154.90
Purchase #7	$51.57	4.439%	$53.8592	$53.86	$53.85	$53.90
7 purchase totals =	$642.69		$693.9033	$693.90	$693.90	$693.90