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	$37.39	9.408%	$40.9077	$40.91	$40.90	$40.90
Purchase #2	$86.51	6.528%	$92.1574	$92.16	$92.15	$92.20
Purchase #3	$154.51	4.517%	$161.4892	$161.49	$161.50	$161.50
Purchase #4	$25.54	3.678%	$26.4794	$26.48	$26.50	$26.50
Purchase #5	$60.92	10.451%	$67.2867	$67.29	$67.30	$67.30
Purchase #6	$63.62	12.416%	$71.5191	$71.52	$71.50	$71.50
Purchase #7	$142.96	9.203%	$156.1166	$156.12	$156.10	$156.10
7 purchase totals =	$571.45		$615.9561	$615.97	$615.95	$616.00