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	$199.75	6.742%	$213.2171	$213.22	$213.20	$213.20
Purchase #2	$115.45	10.323%	$127.3679	$127.37	$127.35	$127.40
Purchase #3	$30.34	3.404%	$31.3728	$31.37	$31.35	$31.40
Purchase #4	$123.73	12.109%	$138.7125	$138.71	$138.70	$138.70
Purchase #5	$79.59	12.288%	$89.37	$89.37	$89.35	$89.40
Purchase #6	$29.67	6.404%	$31.5701	$31.57	$31.55	$31.60
Purchase #7	$6.57	6.426%	$6.9922	$6.99	$7.00	$7.00
7 purchase totals =	$585.10		$638.6026	$638.60	$638.50	$638.70