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	$109.39	9.586%	$119.8761	$119.88	$119.90	$119.90
Purchase #2	$92.36	9.509%	$101.1425	$101.14	$101.15	$101.10
Purchase #3	$56.32	13.771%	$64.0758	$64.08	$64.10	$64.10
Purchase #4	$218.78	3.869%	$227.2446	$227.24	$227.25	$227.20
Purchase #5	$68.61	11.318%	$76.3753	$76.38	$76.40	$76.40
Purchase #6	$41.86	4.788%	$43.8643	$43.86	$43.85	$43.90
Purchase #7	$156.71	5.620%	$165.5171	$165.52	$165.50	$165.50
7 purchase totals =	$744.03		$798.0957	$798.10	$798.15	$798.10