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	$99.71	3.215%	$102.9157	$102.92	$102.90	$102.90
Purchase #2	$46.84	13.512%	$53.169	$53.17	$53.15	$53.20
Purchase #3	$158.39	4.155%	$164.9711	$164.97	$164.95	$165.00
Purchase #4	$74.42	12.258%	$83.5424	$83.54	$83.55	$83.50
Purchase #5	$105.78	12.425%	$118.9232	$118.92	$118.90	$118.90
Purchase #6	$193.95	10.328%	$213.9812	$213.98	$214.00	$214.00
Purchase #7	$74.73	9.587%	$81.8944	$81.89	$81.90	$81.90
7 purchase totals =	$753.82		$819.3970	$819.39	$819.35	$819.40