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	$31.58	6.855%	$33.7448	$33.74	$33.75	$33.70
Purchase #2	$204.52	9.298%	$223.5363	$223.54	$223.55	$223.50
Purchase #3	$116.33	5.735%	$123.0015	$123.00	$123.00	$123.00
Purchase #4	$56.97	8.160%	$61.6188	$61.62	$61.60	$61.60
Purchase #5	$84.71	5.684%	$89.5249	$89.52	$89.50	$89.50
Purchase #6	$87.93	11.252%	$97.8239	$97.82	$97.80	$97.80
Purchase #7	$33.81	8.625%	$36.7261	$36.73	$36.75	$36.70
7 purchase totals =	$615.85		$665.9763	$665.97	$665.95	$665.80