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	$98.65	3.686%	$102.2862	$102.29	$102.30	$102.30
Purchase #2	$106.85	5.237%	$112.4457	$112.45	$112.45	$112.40
Purchase #3	$38.25	8.449%	$41.4817	$41.48	$41.50	$41.50
Purchase #4	$214.50	8.767%	$233.3052	$233.31	$233.30	$233.30
Purchase #5	$103.60	12.576%	$116.6287	$116.63	$116.65	$116.60
Purchase #6	$193.38	9.803%	$212.337	$212.34	$212.35	$212.30
Purchase #7	$74.59	10.241%	$82.2288	$82.23	$82.25	$82.20
7 purchase totals =	$829.82		$900.7133	$900.73	$900.80	$900.60