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	$62.38	13.547%	$70.8306	$70.83	$70.85	$70.80
Purchase #2	$42.71	6.558%	$45.5109	$45.51	$45.50	$45.50
Purchase #3	$152.35	6.603%	$162.4097	$162.41	$162.40	$162.40
Purchase #4	$225.29	9.440%	$246.5574	$246.56	$246.55	$246.60
Purchase #5	$35.78	13.110%	$40.4708	$40.47	$40.45	$40.50
Purchase #6	$31.82	9.725%	$34.9145	$34.91	$34.90	$34.90
Purchase #7	$245.42	3.583%	$254.2134	$254.21	$254.20	$254.20
7 purchase totals =	$795.75		$854.9073	$854.90	$854.85	$854.90