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	$72.87	7.600%	$78.4081	$78.41	$78.40	$78.40
Purchase #2	$235.69	10.854%	$261.2718	$261.27	$261.25	$261.30
Purchase #3	$90.44	8.647%	$98.2603	$98.26	$98.25	$98.30
Purchase #4	$208.80	6.701%	$222.7917	$222.79	$222.80	$222.80
Purchase #5	$230.81	4.141%	$240.3678	$240.37	$240.35	$240.40
Purchase #6	$30.86	10.861%	$34.2117	$34.21	$34.20	$34.20
Purchase #7	$67.72	4.117%	$70.508	$70.51	$70.50	$70.50
7 purchase totals =	$937.19		$1,005.8194	$1,005.82	$1,005.75	$1,005.90