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	$29.54	6.205%	$31.373	$31.37	$31.35	$31.40
Purchase #2	$236.85	6.467%	$252.1671	$252.17	$252.15	$252.20
Purchase #3	$197.80	12.709%	$222.9384	$222.94	$222.95	$222.90
Purchase #4	$64.47	5.325%	$67.903	$67.90	$67.90	$67.90
Purchase #5	$136.93	7.627%	$147.3737	$147.37	$147.35	$147.40
Purchase #6	$29.76	10.228%	$32.8039	$32.80	$32.80	$32.80
Purchase #7	$172.36	3.653%	$178.6563	$178.66	$178.65	$178.70
7 purchase totals =	$867.71		$933.2154	$933.21	$933.15	$933.30