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	$74.38	4.733%	$77.9004	$77.90	$77.90	$77.90
Purchase #2	$210.54	13.342%	$238.6302	$238.63	$238.65	$238.60
Purchase #3	$12.81	3.718%	$13.2863	$13.29	$13.30	$13.30
Purchase #4	$36.92	9.709%	$40.5046	$40.50	$40.50	$40.50
Purchase #5	$167.39	3.790%	$173.7341	$173.73	$173.75	$173.70
Purchase #6	$205.94	6.320%	$218.9554	$218.96	$218.95	$219.00
Purchase #7	$50.67	5.503%	$53.4584	$53.46	$53.45	$53.50
7 purchase totals =	$758.65		$816.4694	$816.47	$816.50	$816.50